SELF-STERILITY IN CHINESE CABBAGE 



YoicHi Kakizaki 

 Saitama-kcn Agricultural Experiment Station Urazva, Saitama-ken, Japan. 



SELF-STERILITY, in a higher or 

 lower degree, is a characteristic 

 quite common to the plants which 

 bear hermaphroditic flowers and yet 

 are habitually cross-pollinated. Plants 

 of this kind show normal fertility under 

 the natural conditions of flowering, but 

 the amount of fruit is greatly reduced 

 when they are self-pollinated artifi- 

 cially. Such seems the case in grasses, 

 clovers, crysanthemums, sun-flowers, 

 some species of Crucifiers, and a num- 

 ber of other genera. A very fine ex- 

 ample of self-sterility is seen in Ulrich's 

 experiment with rye/ 



This characteristic of the plants 

 mentioned above makes it very difficult 

 for plant breeders to obtain self-ferti- 

 lized seed of these species, especially 

 in case such seed is wanted in large 

 quantities. Consequently it is inter- 

 esting and important to study the mat- 

 ter more exactly and to search for a 

 method by which such seed can be 

 produced with greater ease. Bearing 

 this in mind, the author tried an ex- 

 periment last spring with Chinese 

 cabbage, or Pe-tsai, in order to de- 

 termine the effect of various modes of 

 artificial pollination on seed bearing. 



Under natural conditions almost 

 every flower of Pe-tsai gives rise to a 

 normal pod, with the possible exception 

 of a few terminal ones on each inflores- 

 cence. Therefore, it may be assumed 

 that practically all the flowers experi- 

 mented with would have been fertile 

 under normal conditions. With this 

 fact in mind, five different modes of 

 artificial pollination were applied, viz : 



(a) Flowers covered with paraffin 

 bags, but not pollinated artifi- 

 cially. 



(b) Flowers pollinated artificially 



with pollen of the same flowers. 



(c) Flowers pollinated with pollen 



from different flowers in the 

 same inflorescence. 



(d) Flowers pollinated with pollen 



from different inflorescences on 

 the same plant. 



(e) Flowers pollinated with pollen 



from different plants. 



The following remarks also must be 

 made as to the technique of the ex- 

 periment: (i) All of the flowers under 

 control, whether used as male or fe- 

 male in the cross, were covered with 

 paraffined bags before blooming in 

 order to protect them from fertiliza- 

 tion by pollen-bearing insects. (2) 

 Those treated with pollen from other 

 flowers (c, d, e) were not emasculated, 

 in order to avoid the experimental 

 errors which might have been caused 

 by faults of the operation. In doing 

 so it was assumed that ovules of a 

 flower would be more readily fertilized 

 by pollen from other flowers, espe- 

 cially that from different plants, than 

 with its own pollen ; in other words, 

 the pollen of a flower would actually 

 be more or less handicapped in compe- 

 tition with that from different flowers 

 or plants. (3) After pollination, the 

 flowers were kept under the paper 

 covering for a few days. This treat- 

 ment did not seem injurious to the 

 development of the pods, because it 

 was found that there was no essential 

 difference in fertility between the flow- 

 ers which were artificially pollinated 

 with pollen from different plants, and 

 those left to natural cross-pollination. 



^ Ulrich, K. Die Bestaubung und Befruchtung des Roggens. Inaug. Diss. Halle, 1902. 



.374 



