!7J: 



PLANT STUDIES 



;:^ 



leaves expanded to the air and sunlight, the plautlet has 

 become independent (Fig. 331). 



It must not be supposed that all of tlie details just 

 given apply to tlie 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 tlie 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 Avliich covers it. In such a 

 case tlie cotyledon is never un- 

 folded, but remains as an absorbing 

 organ, while the root extends in 

 one dii'cction, and the stem, with 

 its succession of unsheathing leaves, 

 develops in the other. 



248. Summary from Angiosperms. 

 — At the beginning of this chapter 

 (§ 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), cliicfly l\y insc(^t pollination, 

 is l)r(night into contact with the stigma, whicli is a recep- 

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



Fri;. 331. Scedlingof liazcl ( Car- 

 /n/"fs). showing primary root 

 (/nv) beriring rootlets {,svr) 

 upon which arc iiiinu'roiis 

 root hairs (/■). liyiiocoty] (A), 

 cotyji'dons (r), yoiniL,^ stem 

 i' I, inid lirst (/I and second 

 (/') true leaves. — After Scuim- 



I'EK. 



