COTYLEDONS. 



599 



and their role of nurse is at an end. Often, indeed, the cotyledons take on 

 later another function, but they have cea.sed to be of importance as reserve- 

 tissue for the use of the developing embryo. In those instances where the 

 supply of food given by the parent plant is not stored up in the cotyledons. 



Fig. 141.— Cotyledons. 



> Longitudinal section of seed of Iticintis, parellel to the plane of the embryo. 2 Longitudinal section of the same seed, taken 

 at right angles to the two parallel cotyledons. « Longitudinal section through a grain of Wlieat (Triticum vutgare); x 4. 

 4 Longitudinal section througli a grain of Wheat after germination has talcen place ; x 4. ^ Ttie embryo witl) its scntellum 

 in a grain of Wheat ; x 80. « Absorbent cells on the surface of the scutellum of a grain of Wheat; x 210. ? Germinating 

 seed of the Corn-coclde (A^osUmma Githago) ; sliglitly magnified, s Longitudinal section of the same. " .Seedling of the 

 Com-coclile in a later stage of development 'o xhe same in longitudinal section. " Absorbent ceils on the surface of 

 the cotyledon adjoining tlie reser\'e-tissue in the seed of the Corn-cocltle ; x 210. 12 Germinating seed of Tradescantia 

 V\rginica\ slightly magnified. »» The same iu a later stage of development. » Transverse section tlirongh tlie Itnob- 

 lilce end of tlio cotyledon of TratUscantia Virginica embedded in the reserve-tissue ; x 10, le Absorlient cells on tliu 

 surface of this Icnobdilce end; x 180. *« Germinating seed of the Onion {Allimn Cepa); natural size. 1' Tlie same cut in 

 half; slightly ma^itled. >■> Seedling of the Onion in a later stage of development ; natural size, i^ The same cut through 

 loDgitudinally ; slightly mag uifled. 



but is deposited as a special reserve near the embryo, its nourishment is more 

 complicated. 



In this state of affairs the cotyledons have an essentially different function. 

 They serve as agents, and their first task is to take up the building-materials. 

 These have been liquefied in the reserve -tissue, either by changes in that tissue 

 itself, or by the direct solvent action of the cotyledons. They are then conducted 



