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A TEXTBOOK OF THEORETICAL BOTANY 



Fig. 1436. — Section of a germinating Wheat grain. The 

 embryo is on the left, the scutellum in the middle and 

 the endosperm on the right. Digestion of the endo- 

 sperm is proceeding from the surface of the scutellum. 



enlarges to a mushroom-shaped mass which invades and destroys all the 

 endosperm. It is connected by a stalk or middle piece to the sheathing base 

 of the cotyledon, which surrounds the plumule in the developing plantlet 

 outside the seed. In Cocos nucifera the endosperm is hollow and the haust- 

 orium enlarges to fill the entire space. It is a mass of soft white tissue as big 

 as an apple, contacting the endosperm all round its surface and remaining 

 active and absorbent for several years, as is commonly the case in the Palm 

 family (Fig. 1438). The middle piece is very long, 40-50 cm., so that the 

 seed and the embryo are far apart. Indeed in some Palms, the middle piece 

 has been known to rise above ground, bearing the seed with it, at some 

 distance from the rest of the young plant. 



The two Palm genera Nipa and Phytelephas differ markedly from all 

 other Palms in that the haustorium is formed from the primary root. The 

 cotyledon consists only of a short sheath and the root enlarges to fill the 

 big hollow space in the middle of the endosperm. The result of this 

 peculiarity is that it is the plumule, not the radicle, which emerges first 

 from the pericarp in which the seed is enclosed (Fig. 1439). Adventitious 

 roots spring from the cotyledonary axil and bend downwards into the ground 

 like stilts. The state of affairs in Nipa is connected with the usual Palm type, 

 and indeed with the Grass type, by certain other Palms {Thrinax, Onco- 

 sperma) in which the primary radicle, though external to the seed, forms 

 no root hairs and is quickly replaced by endogenous adventitious roots 

 from the short hypocotyl. 



In many seeds and fruits there exist special structures concerned with 



