1. Abnormalities in pollen development under natural conditions were statistically investigated in five species of Crinum, C. asiaticum var. japonicum, C. latifolium, C. gigas, C. Moorei and C. sp. (Powelli?, pink-flowered), because of the necessities, 1, for the analysis of the experimental disturbances and climatic influences upon the pollen development, 2, for the cytological analysis of the hybridity.
2. In the genetically homologous species, dwarf, giant and sometimes twin pollen grains are formed in very low percentages (see the first table).
3. Examination of pollen tetrad formation showed that most of the dwarf grains were derived from both pentads and hexads, and the giant were from monads.
The mode of polyad formation in several cases suggests that those abnormalities of low frequencies in the genetically homologous individuals may be ascribed to an accidental failure of balance among the physical and chemical conditions in a few pollen mother cells, which has been caused by interactions of those conditions in the course of meiosis, rather than to the presence of slightly heterotypic nature in chromosomes of those individuals.
4. In C. asiaticum var. japonicum and C. latifolium, the abnormal grains appeared in a close proximity of their frequencies in one case, as seen in the following table:
This fact seems to support the hypothesis advanced above (3).
5. In the species which is expected to be of hybrid origin, abnormal pollen grains appear in very high frequencies, and viable and normal grains in very low (see the following table):
In addition to it, there are certain extreme abnormalities among them which could not be found in the homologous individuals, such as ultra-giant pollen grains, giant twin grains, 3-nucleate and 4-nucleate grains. Though these abnormalities can not be expected as induced by only the failure of the pairing of the chromosomes in the first meiotic division, most of the abnormal dwarf grains may be apparently expected as induced by it. So, it may be said that the abnormalities in the pollen development in a hybrid species must be discussed from more than one point of view.
