Relation of the Enclosing Structure of the Digitaria Adscendens Spikelet to Its Germination : II. The role of the enclosing structure (glumes and shell coat) ofcrab grass (Digitaria adscendens) and rice-plant spikelets in the absorption of water and water soluble substances

[摘要] After-ripened (awakend from dormancy) spikelets of D. adscdndens were placed in a germinating bed at 30°C; after five hours they absorbed an amount of water, 25 per cent of their initial weight; after 20 hours; 42 percent; and after 60 hours, 45 percent; then started to germinate. Dormant spikelets absorbed a smaller amount of water than the after-ripened ones and did not germinate. The removal of the enclosing structure (glumes and shell coat) of the after-ripened spikelets promoted their germination. The enclosing structure of the spikelets having great water holding capacity absorbed water rapidly when placed in the germinating bed, thus it inhibited the water absorption of the embryo; being closely related with the germination of the spikelets. In the methylen blue and iodine tests, these substances penetrated into the embryo end of the caryopsis via the funiculus, and spread further laterally and distally. The staining speed ofthe caryopsis of the spikelet soaked in methyen blue solution was slower than that of the caryopsis which was soaked in the solution after the removal of the enclosing structure of the spikelet (Fig. 1). In the iodine test, the inhibiting power of the enclosing structure of the spikelets on the absorption of iodine water was stronger in the dormant stage, and became weaker with the increase in the length of storage period, and at last an easy absorption was followed. As to the spikelet stored for 172days after the havest, being immersed in a iodine water and after that examined the colour of its caryopis by removing the enclosing structure, it was found that the iodine translocated mainly through the funiclus into the embryo end of the caryopsis and then moved distally (Fig. 2). However in the case of the spikelet stored for 350 days, both the distal and embryo ends of the caryopsis were stained by the iodine, especially the former was far darker. Seemingly between the palea and lemma at the distal end of the spikelet of about this age a crevice was made and through which the entry of iodine water into the caryopsis was permitted. Rice spikelets stored for 271 days were coated by paraffin, in various ways so that differnt regions of the spikelets were exposed, and were soaked in P32 solution. It was found that P32 scarcely entered through the general surface of the spikelet but entered to a small dgree through the line where the palea and lemma layers overlap. But P32 entered mainly via the rachilla and funiculus into the embryo end of the caryopsis, whence it spread laterally and distally (Table 1). But when only a very little part of the distal end of the enclosing structure was exposed, the iodine penetrated only through the exposed part and spread to the embryo end (Table 2). In the iodine test, this substance was absorbed from the embryo end or distal end of caryopsis, and first diffused to the some cell layers existing inside of the seed covering, and then spread gradually into the central part of caryopsis. And in the P32 test it seemed that P32 distributed also at outer part of caryopsis as soon as is was absorbed, because there was little difference of P32 counts among 3 parts of the caryopsis namely embryo end, distal end and remaining portion (Table 2). From the results above mentioned it will be concluded that the enclosing structure absorbes water and other water soluble substanses rapidly, preventing their penetration into the direction of the embryo by storing them. Thus the enclosing structure controls the dormancy of the embryo and the germination of the spikelets. On the other hand, besides the physical protection to the caryopsis the enclosing structure is effective to determine the passage way of the water and other substances to the embryo and thus to protect the embryo from attack by microrganisms. [the rest omitted]

[学科分类] 农业科学（综合）