374 



PLANT STUDIES 



j-t^- 



leaves expanded to the air and sunlight, the plantlet has 

 become independent (Fig. 331). 



It must not be supposed that all of the details just 

 given apply to the germination of all seeds, for there are 

 certain notable variations. For ex- 

 ample, in the pea and acorn the 

 cotyledons, so gorged with food as 

 to have lost all power of acting as 

 leaves, are never extricated from 

 the seed-coats, but the stem tip. 

 which lies between the cotyledons, 

 is pushed out by the elongation of 

 the cotyledons at base into short or 

 sometimes long stalks. In the ce- 

 reals, as corn, wheat, etc., the em- 

 bryo lies close against one side of 

 the seed, so that it is completely 

 exposed by the splitting of the thin 

 skin which covers it. In such a 

 case the cotyledon is never un- 

 folded, but remains as an absorbing 

 organ, while the root extends in 

 one direction, and the stem, with 

 its succession of unsheathing leaves, 

 develops in the other. 



248. Summary from Angiosperms, 

 — At the beginning of this chapter 

 (S 237) the characters of the Gym- 

 nosperms were summarized which 

 distinguished them from Angio- 

 sperms, whose contrasting charac- 

 ters may be stated as follows : 



(1) The microspore (pollen- 

 grain), chiefly by insect pollination, 

 is brought into contact with the stigma, which is a recep- 

 tive region on the surface of the carpel, and there de- 



Fig. 331. Seedling of hornbeam 

 (Carpinus), showing pri- 

 mary root ihw) bearing root- 

 lets (sw) upon which are 

 numerous root hairs (r), hy- 

 pocotyl (h), cotyledons (c), 

 young stem (e), and first (/) 

 and second {I') true leaves. 

 — After Schisiper. 



