A mature trichome is twenty to forty times the size of the epidermal cell from which it arises. All parts of the cell show a correlative increase in size. The nucleolus may become several times the size of the unmodified epidermal nucleus. The pro-chromo-somes, the permanent bodies of the nuclear picture, often become as large or surpass the size of the nucleus of their origin. The original homogeneity of the pro-chromosomal material is retained in the exaggerated ones and there can be no question of division of the chromomeres to account for their increase in size. Increase in size is due to a distension of constituent parts. Living nuclei show no organization save for the nucleolus. Severe mechanical handling and treatment with aceto-carmine crystallize out a nuclear organization otherwise invisible. Therefore fixed and stained material showing nuclear organization arouse the suspicion of artefact. Trichomes may be classified with glandular structures in insects and may be placed in the category of physiological manifestations seen in. the salivary glands of some dipteran larvae. The organization of the germ cells of Mercurialis annua. cannot be deduced from the enlarged nucleus of the trichome. On the contrary the new function assumed by the developing trichome seems to impress itself an the whole cell and its form becomes a visible to the eye expression of forces that cannot be evaluated in terms of the visible. The nucleus of the trichome can no longer be regarded as a directing agency of the cell but it has become a passive organ caught in the current of function. It is buffeted about at will and becomes misshapen and distorted by forces which it may have previously controlled.
1. The chromatin reticulum is granular in character and is more or less evenly spread out in the nuclear vacuole. 2. The chromatin threads during the heterotypic prophase radiate in various directions and there is no regular parallelism. 3. The synizesis is due to the gradual contraction of the reticu lum and growth of the nuclear cavity. 4. The spireme formed during the synizetic contraction is doubled in some places only and single in the other portions. 5. During the loosening of the spireme from the synizetic condition beautiful loops, more or less equal to the gametic number, are formed. 6. Following the distribution of the spireme in the form of loops in the nuclear cavity and the separation of the individual loop by segmentation, the second contraction orsynapsis takes place. 7. The pairing of the two arms of the loops, representing the two univalent chromosomes is evident. 8. The nuclear membrane and the nueleolus disappear simultaneously, while the multipolar spindles suddenly appear. 9. The number of the chromosomes in the haploid phase is 40. 10. The bivalent ehromosomes are more or less the Same in shape and size. 11. The heterotypic division takes place in a normal manner, no lagging or other irregularity was observed. 12. The daughter nuclei do not pass into resting stage as usual but pass directly into a normal homoeotypic division, forming the four daughter nuclei of the pollen grains.
1. The investigation of 9 species and varieties of Spinacia revealed that each of the types examined contained 2 relatively large pairs of somatic chromosomes with sub-median spindle fiber attachment constrictions, 2 medium sized pairs with sub-terminal attachment constrictions, and 2 relatively small pairs with subterminal constrictions. One of the small pairs is characterized by the presence of trabants an the shorter arm. There is thus no cytological evidence to suppart the view that Spinacia oleracea L. and the so-called S. tetandra Stev. are distinct species. An examination of the chromosome complements of male, female and intersexual plants failed to reveal any heteromorphic allosomes. The metaphase chromosomes of the dermatogen of Spinacia are characterized by an affinity between homologues and by widely divergent chromatids. 2. The chromosome numbers of 4 species of the Chenopodiaceae, hitherto uninvestigated somatically, are as follows: Sueda linearis Moq., 2n=54; Kochia scoparia L., 2n=18; Salsola Kali L. var. tragus L., 2n=36; Chenopodium ambrosioides L., 2n=32. The chromosome situation in the Chenopodiaceae, so far as investigated, appears to be based an the number x=9, rather than x=3, although the former number may have been secondarily derived from the latter. A reduplication of an original 3 might conceivably account for the chromosome situation in Spinacia. 3. Somatic doubling of the chromosome complement was found to occur in the periblem of the root tip in Kochicc scoparia and in each of the species and varieties of Spinacia investigated. 4. The results of a statistical investigation reveal that: (a) There is an apparent decrease in the length of the prophase period relative to that of the metaphase period from the periphery to the center of the root tip in Spinacia. The prophase is relatively longest in the dermatogen, shorter in the periblem and shortest in the plerome. (b) In the region of somatic doubling in the periblem of Spinacia the duration of the prophase period relative to that of the metaphase period is apparently no longer in instances where the chromosomes are paired than where they are unpaired; and that if the prophases with paired chromosomes are actually of longer duration than the prophases with unpaired chromosomes in point of time, then the metaphases with paired chromsomes are longer than the metaphases with unpaired chromosomes. 5. Certain observations which were out of harmony with the hypothesis held by previous investigators to explain somatic doubling in Spinacia have led to the development of a new hypothesis which takes into account these formerly anomalous observations. This hypothesis is based an the conception that chromosomal division and nuclear division are not always interdependent, but may be influenced by environmental factors so that they behave in an asynchronous manner. The division of the chromosomes and the separation of the division products occurring at a faster rate than the division of the nucleus as a whole, ultimately results in two chromosomal cleavages occurring within one nuclear cycle. When this occurs the chromosome number is doubled. On this hypothesis the freauency with which doubling occurs and the height to which the chromosome number mounts are dependent upon the rapidity of the development of the environmental factors which distort the normal synchronism of nuclear and chromosomal behavior. If this development begins in or very near the promeristem and progresses rapidly it may result in the formation of octosomatic cells before the natural cessation of meristematic activity in the oldest part of the root tip occurs.
1. Seven varieties of rice plants have been cytologically examined. The chromosome number in each is determined as 12 haploid, 24 diploid. Satellites and secondary constrictions are not found in the chromosomes. 2. In the somatic prophase a pair of chromosomes with terminal knob-like bodies remain attached by the knob to two Small nucleoli or one large nucleolus which results by the fusion of the two. These knobs must be concerned in the growth of the telophase nucleoli. 3. The resting nucleus of the pollen mother-cells generally has a single nucleolus with no crystalline bodies. 4. The leptotene thread is split like the somatic early prophase chromosomes, the two chromonemata being closely twisted about each other. 5. During the heterotypic prophases the nucleoli, one or two in number, remain closely connected with a particular pair of chromosomes at one end (referred to as the nucleolar body) from the leptotene stage until the nucleolus disappears completely at metaphase. 6. During synizesis the nucleolus in some of the nuclei of the varieties studied produces a bud, which grows until the two nucleoli attain the Same size at early diakinesis by transfer of material from the larger to the smaller. 7. Comparison of six varieties of rice shows no difference in the size of the nuclei and nucleolar contents. But it shows a significant difference in the size of the nuclear diameter in those cells with one nucleolus at diakinesis and with two (Table 1). This is correlated with the differences in the size of the nucleolar diameter when one nucleolus or two are present at diakinesis. Only the larger nucleoli (which are present in the larger nuclei) bud, and the “budding” takes place after the maximum size of the nucleolus is reached. 8. Budding of the nucleolus may be due to the relative increase of the nucleolar material within the mother nucleolus or it may be an artefact produced by the treatment. When budding takes place it is always at the point of attachment of the terminal chromosome knob. 9. The method of chromosome pairing is parasynaptic, pairing commencing at the ends of the chromosomes. Variation in size and shape of the 12 bivalent chromosomes is found in early diakinesis, one larger twisted pair being particularly noticeable. 10. From resting stage until early diakinesis there is an increase in the size of the nucleolus, followed by a gradual decrease from late diakinesis with the gradual condensation of the chromosomes until the time of its complete dissolution at metaphase. 11. It is concluded that the nucleolus contributes matrix substances (not chromatin) indirectly to all the chromosomes, which is carried over by metaphase and anaphase chromosomes, and a definite nucleolus is organized at telophase from this substance under the influence of the nucleolar body present an the end of one chromosome of the haploid complement. Trivalent and univalent chromosomes are sometimes found at diakinesis in certain Japanese varieties. 12. The phenomena of cytomyxis, pollen mother-cell fusion, binucleate and tetraploid pullen mother-cells and failure of cytokinesis during meiotic divisions of some of the microsporocytes, are described. As the result of these aberrations, diploid gametes are formed, which will account for the origin of triploid and tetraploid plants of rice. 13. The origin of the nucleolus is discussed and its relation to the nucleolar body; also the possible rôle of the nucleolus in inheritance. 14. It is emphasized that further studies of a biochemical nature are required before definite conclusions may be drawn as to the relationship between the matrix substance of the ehromosomes and the nucleolus. This work was carried out in the Botanical Department of King's College, University of London. The author wishes to express his indebtedness and sincerest gratitude to Professor R. Ruggles Gates, under whose supervision this work was done
1. The cytology and micromorphology of Lycopersicum esculentum, and L. pimpinellifolium and their hybrid were studi, ed. A comparative study was also made of 10 small-fruited cultures from various parts of the world. 2. Chromosome behavior in both species was normal. L. pimpinellifolium had somewhat fewer chiasmata than esculentum. 3. The hybrid was cytologically regular except for certain constant weaknesses of pairing at pachytene and a much reduced chiasma number throughout. 4. In the following micromorphological characters pimpinellifolium was significantly smaller: pollen size, chromosome size and volume, both somatic and meiotic, size of cell and nucleus in root tips, and size of stoma. 5. Flower parts are constantly five in pimpinellifolium. In esculentum they are variable but usually six or seven. 6. Three of the 11 cultures from foreign locations were true L. pimpinellifolium; the rest were small-fruited L. esculentum. 7. Secondary association is considered of no significance in the tomato. I wish to express my gratitude to Dr. E. W. Lindstrom, head of the Department of Genetics at Iowa State College, for the use of his tomato cultures and for his advise and helpful criticism in the performance of this investigation.
1. Hybrids between P. somniferum and P braeteata were produced, the former being used as female parent. The F1 plant appeared intermediate with respect to several characters, though with some matroclinic tendencies. 2. Some characters (laciniate petals, hairy peduncles, duration of life etc.) of P. somnif erum which are recessive in the F1 plants of somniferum×orientale, were found to be dominant in the F1 plants, of sonniferum×braeteata. In relation to this faet the cumulative effect of genes is discussed. 3. The number of the somatic chromosomes in the F1 plant is 18, i.e. the sum of the haploid chromosome numbers of both parents (11 and 7). 4 bivalents and 10 univalents- were observed in the diaphase of the PMC. This fast is in conformity with the view that the haploid chromosome constitution of P. somniferum is 4II+3I and that there are no homologous chromosomes between P. somniferum and P. braeteata. 4. The chromosome behaviour in the meiotic phases of the PMC of the F1 plant is very irregular, espeeially that of the univalent chromosomes. In different anthers different kinds of irregularities in chromosome behaviour were found. In some anthers there were observed many PMCs, in each of them all the separated halves of the bivalents, or some of them, formed a small nucleus, and the remaining chromosomes formed a large nucleus after the ist meiotic division. The temperature effect of the season an the meiotic division is suggested. 5. In the interphase nuelei in some PMCs, the 4 ehromatids in each of separated halves of bivalents and each of unseparated univalents and 2 chromatids in each separated univalent were clearly observed. The individual chromatids coiled spirally and twisted around each other. They may separate from each other in the first nuclear division of the pollen grains. In some of the chromosomes which consist of two pairs, of chromatids, chiasmata were observed. Here I wish to express my best thanks to Hon. Prof. K. FUJII, for his valuahle advice throughout the course of these studies. The expense of carrying out the present work was partly defrayed out of a grant from the Japan Society for the Promotion of S.cientific Research, to which my thanks are due.