On the Depth of the Creases on Rice-Kernels.

Abstract

There are five creases or grooves on a rice-kernel, extending its entire length-two facing fitting lines of the edge of lemma and that of palea, one facing the keel of palea and two facing about midway on both sides of lemma. Of those five creases or furrows, the two facing fitting lines of lemma and palea are deep. Therefore, those two creases only are measured in depth by the writers in the present experiment. (Besides those, one facing the keel of palea is also distinct.) When rice-kernels are milled, the bottoms of those deep creases are not easily skinned. Thus, we sometimes perceive yellow lines of remnants of bran on kernels skinned imperfectly. (ref. Fig. 1 and Fig. 2) Shallow creases are desirable, because the deeper the creases are, the more potion of a kernel has to be removed, to obtain perfectly white rice. (ref. Fig.6) Therefore, the depth of creases affects the relative difficulty of skinning as well as the percent of loss by skinning. The depth of the creases (A₁ and A₂ in Fig. 5) on kernels of several varieties are measured. The same measurement is taken on kernels at different stages of ripenning as well as those grown in different stages of fertility. The methods used for the measurements are explained briefly. Rice-kernels are cut with a sharp razor, midway along the length. To measure the depth, the cross section is brought under a microscope equipped with an ocular micrometer and is moved to such a position as shown in Fig. 5. To get the depth of the creases of a kernel, the mean of the depth of two creases A₁ and A₂ in Fig. 5 is computed. From these experimental results, the following facts are seen. They are summarized as follows:- The depth of the creases of kernels varies distinctly with the variety of rice. (ref. Table 1∼Table 4) Consequently, the writers suggest it should be considered one of the important varietal characteristics which must be examined to qualify a variety for a superior one in the case of rise-plant breeding. The crease is shallower two thirds upward from the embryonic end than midway. Midway it is shallower than one third from the end. Those results show that the crease is not always of the same depth along the entire length. Therefore, measurements in depth of creases should be taken at definite positions of a kernel in the case of varietal comparisons. (ref. Table 5 and Table 6) As mentioned above, the depth of creases is not only a varietal characteristic, but also it is influenced by the growth conditions. Immature kernels have deep creases. They become shallower as maturity proceeds. (ref. Table 7 and Table 8) Because of this, it is necessary to harvest crops when they are quite ripe. The creases of kernels grown under imperfect conditions of fertilizers are deep. (ref. Table 9 and Table 10) Thus, it is necessary to get good fertilizing conditions, to raise rice crops of good quality. As it is naturaly supposed that rice-kernels grown under poor conditions of soil and cold climate have deep creases, it may be said that their skinning is difficult and the percent of loss by skinning increases.