ANATOMY AND PHYSIOLOGY OF PLANTS. 245 



36. The vitellus is an organ of a fleshy but firm tex- 

 ture, situated, when present, between the albumen and 

 embryo ; to the former of which it is attached only by 

 adhesion, but to the latter by incorporation of substance, 

 so as to be inseparable from it except by force. 



The vitellus is said not to rise out of the earth during germination ; 

 but like the albumen, seems destined to afford nutriment to the 

 embryo. 



37. The embryo is the most essential part of a fertile 

 seed, considered to be formed from a more or less per- 

 fect mediilary point, called the corculum, which exclu- 

 sively forms the nova progeneis, or new plant, and to 

 which all the other parts are added for its temporary 

 use only. It is commonly said to consist of the cotyledon, 

 radicle and plumelet. 



38. The cotyledon or seed-lobe is a very necessary 

 portion of the seed, which, together with the radicle and 

 plume, form the body of the embryo. 



Some seeds are said to be without this part, and hence called nco- 

 ttfledones ; others have one, called monocotyle.dones ; a third set, 

 dicotyle dones, have two lobes ; while those seeds having more than 

 two lobes, are denominated polyrotyle dones. 



39 The cotyledons, in the most perfect seeds, are 

 formed of cellular tissue, through which vessels arc 

 every where distributed, covered with a very fine pelli- 

 cle or coat, which prevents their adhering to each other 

 or the plume. The cells of the cellular structure are 

 generally filled with albumen. 



The cellular structure of the cotyledon is well displayed in a slice 

 Y2 



