PHJENOGAMIA. 



161 



a rudimentary root at the other (Fig. 277, r.d). The 

 embryo-sac develops within it a mass of cells, called the 

 endosperm, at the expense of which the embryo, or 

 rudimentary plantlet, grows. The ovules become much 

 enlarged while the embryo is forming, and their outer coat 

 generally becomes thickened and more or less hardened. 

 At this stage it is called the Seed, and at maturity sepa- 

 rates from the parent 

 plant. 



182. After a period 

 of rest, the seed, ex- 

 posed to suitable condi- 

 tions, germinates ; that 

 is, when proper tem- 

 perature and moisture 

 are supplied, it begins 

 anew its development. 

 It draws on the store of 

 nourishment contained 

 in the endosperm, or 

 cotyledons ; the caulicle 

 elongates ; the radicle, clothed with the root-cap (Fig. 277a, 

 R.C.), grows downwards; and the stem, surmounted by the 

 plumule (Fig. 211,1, pi), grows upwards. By the time 

 the nourishment contained in the seed is exhausted, the 

 -plantlet (Fig. 277, III) is able to absorb food from the 

 soil, and it develops by successive internodes into the adult 

 form. The three tissue systems are well developed in the 

 Phasnerogamia. The epidermis is supplied with numerous 

 stomates ; and trichomes of various forms are also copiously 



Fig. 27Ya. Section through the end of a root, highly magnified, and showing the 

 root-cap {R.c.)', i, i, initial cells; D, dermacogen; Per, periblem ; Pier, ple- 

 rome. 



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