370 Johnson : Development of Saururus cernuus L 



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first noticeable change in the seed is a swelling of the endosperm, 

 which finally burst through the seed coats at the top and projects 

 through the rent in these and the carpel as a white papilla (cp, 

 Figs. 7, 9). This swelling enlarges the cavity occupied by the em- 

 bryo in the endosperm and soon the embryo shows signs of re- 

 newed development. The root end elongates and the cotyledons 

 grow downward and bend together at the ends (em, Fig. 7). 

 Still later the root of the embryo pushes through the tip of the 

 endosperm papilla till finally everything but the cotyledons is free. 

 The latter remain tightly grasped by the collar-like end of the en- 

 dosperm papilla, and reach at first not nearly to the bottom of the 

 cavity in the latter (cot, Fig. 8). 



During this time the only change in the relation of the endo- 

 sperm and perisperm is that the former pushes down slightly into 

 the large lower endosperm cell or sac (ep, Figs. 7, 8). As develop- 

 ment goes on the hypocotyl elongates, pushing the root down 

 into the soil, and the cotyledons stretch to push the stem growing 

 point well out of the seed in one direction (cot, Fig. 9), while their 

 tips push inward and thicken to force the endosperm which 

 covers their tips like a cap, down against the tissue of the peri- 

 sperm (cot, ep, psp, Fig. 10). The latter is gradually broken down 

 by the encroaching endosperm, till in the later stages of germina- 

 tion it forms a second cap over the cotyledons outside the endo- 

 sperm (psp, Fig. 10). After the root penetrates the substratum the 

 hypocotyl continues to elongate and thus the whole fruit is raised 

 into the air supported by the cotyledons (Fig. 9). The latter be- 

 come broadly ovate, with only the narrow thick tip enclosed by 

 the endosperm, and separate at the base to allow the plumule, 

 which is now formed, to push its way out. 



In the latest stages just before the fruit drops from the coty- 

 ledons the endosperm consists of a thin layer of compressed cells, 

 without noticeable nuclei or other contents. Though the tip of 

 the endosperm which projects out of the seed is exposed to the 

 light, there was no indication that functional chloroplasts are ever 

 formed. 



The perisperm is either similarly flattened against the integu- 

 ment, or, in other cases, the cells seem to be emptied of their starchy 

 contents while the walls retain their former shape. Whether the 

 endosperm plays any part in the secretion of an enzyme for the 



