STUDJES OF SEED-PLANTS 153 



flowers of the ordinary flowering plants, and they will be 

 described later ( 211). 



142. The Work of Cotyledons. It is evident from the 

 seedlings studied in the laboratory that cotyledons have 

 several kinds of work. (1) They may become leaf-like 

 and for a time serve as leaves (squash, sunflower). (2) They 

 may be simply store-houses of food materials and without 

 the functions of ordinary leaves, not even getting out of the 

 soil (pea, acorn). (3) They may be of use only as an organ 

 for digesting and absorbing food stored in endosperm around 

 the cotyledons (corn). (4) Some cotyledons combine func- 

 tions 1 and 2. As an example, the bean cotyledons become 

 green and do some work as leaves, and also are stored with 

 food. This is true in all seedlings which have very thick 

 green cotyledons rising above the ground and no endosperm. 

 (5) Functions 1 and 3 may be combined. For example, the 

 cotyledons of the castor-oil seed and onion are leaf-like, 

 but they remain in contact with the endosperm until it 

 has been absorbed. This is the case in all seedlings with 

 cotyledons which rise above the ground, with endosperm 

 in the seed, and with the seed-coats pushed out of the soil 

 and remaining around the endosperm until it is absorbed. 



Observe, when opportunity offers, seedlings of various wild and 

 cultivated plants. It will be interesting to reserve a page in your 

 note-book for "Work of Cotyledons" and make records in five 

 columns headed as follows: (1) As Leaves ; (2) For Food-storage; 

 (3) As Absorbers ; (4) As Leaves and storage ; (5) As Leaves and 

 absorbers. (The numbers refer to those used above.) 



Cotyledons are usually equal in size, as in bean and squash 

 seedlings; but in some species of plants one is larger than 

 the other. In some cacti both cotyledons are exceedingly 

 small (rudimentary) ; and in still other seeds only one coty- 

 ledon is rudimentary. 



143. The Epicotyl. The epicotyl (sometimes called 

 plumule) is found well developed in some seeds before germina- 



