Embryological Studies on Mote-Formation in Cotton.

Abstract

It was confirmed that the checking of seed development or the mote-formation in cotton occurs with numerous forms at various stages or perhaps at any stage in development beginning from the day of flowering and even prior to flowering. So far as this investigation is concerned, the following factors have been observed. The materials studied were each one variety of upland and Chinese cotton. 1. The ovule itself was defective and failed to receive pollen-tube. In this case are involved the ovule in which the embryosac is thoroughly lacked and replaced by nucellus (Fig.2) and also ovule in which the embryosac is located but the egg cell, synergids and polar nuclei therein are either misplaced and hot organized (Fig.5), while in other ovule they are shrunken (Fig.4). Each instance should be undoubtedly induced prior to the day of flowering. 2. The ovule was normally formed, but the pollen-tube although reaching to ovule failed in completing the fertilization. Two stages could be identified in this case, namely, failure of pollen-tube to enter into embryosac (Fig.6) and failure of male gametes which entered into embryosac to fuse with the female gametophyte (Fig.7). All of them were observed in bolls or 4∼7 days after anthesis. The male gametes as well as female gametophyte remained unharmed without degeneration in every case. The failure of ovule to receive pollen-tube due to defective pollination, insufficient supply of pollen grains and so forth was not disregarded herein, but within the extent of this experiment no applicable cases were found. The abortive seeds of this kind might be expected to occur with the much frequency as suggested by previous investigators. 3. The fertilization was normally functioned but the successive development of ovule was arrested to grow into normal seed (Fig.8∼11). The occurrence of motes induced for the above No.1 and No.2 reasons appears to be relatively very few, but to be the source responsible for formation of typical small-motes. Meantime, the majority of motes produced in cotton boll appear to depend upon No.3 case in general. Different stages of development forming a graduated series were involved in this case, but for the most parts they appear to arrest at the comparatively very early stage and to result in developing into tiny structure of small-motes. The mote-formation due to the bollsucking insect injury was out of consideration, since here was lacked in insects of this kind. In addition, some observations were made on the variation of mote occurrence with position in locks. The procedure in obtaining the position data employed was similar to PEARSON'S idea classifying the locks as to size, but differed in classifying the ovules in two groups further according to placental ridges with which the ovules are found to attach in line. More consistent tendency was obtained in that the mote production for tip positions was smaller than that for the basal ones in upland cotton as compared with that of previous reporters, while the situation was slightly the reverse in oriental variety (Table 2). The false motes were excluded from counting the mote numbers. They were frequently found in upland variety, but no presence was recognized in oriental one.