124 



THE CTYPTOGAMIA OB FLOWKRLE88 PLANTS. 



620. The cause op the downward tendency op 

 THE ROOT is d theme of much discussiou. Some have 

 referred it to the principle of gravitatioQ : others to its 

 supposed aversion to light. But it is a simple and satis- 

 factory explanation that its growth or cell-development 

 takes place most readily on the moist side of its growing 

 point, and consequently in a downward direction, so tong 

 as the soil in contact with its lower surface is more moist 

 than that above. Hence also the well-knov^n tendency 

 of roots toward springs and water-courses. 



CHAPTER XV, 



THE CRYPTOGAMIA OR FLOWBELESS PLANTS. 



621. Distinction of parts. In the lowest 

 of the Cryptogamic tribes the organs of vege- 

 tation and of repi-oduction are the same. Each 

 cell in the structure grows, nourishes, multiplies. 

 Higher in the scale we find a gradual specializa- 



4S6, A Tree Fern (of the Island ^ . j ■ ^-u -l ■ i . •, 



ofJavo), 40 feet in height tion of organs, and m the higher tribes, as m 



A Fern, Polypodlmn 

 viilgare. 4S6, Its frond, 



457, Lobe of the fiond en- 

 larged, showing the eori, 



458, One of the eoii (mag- 

 nified) consisting of ninny 

 sporangi. 489, One spor- 

 ange (further magnified) 

 bursting and discharging 

 the spores. 490, A spore. 

 491, Spores beginning to 

 germinate ; and 492, 493, 

 producing the prothaUvs 

 with rootlets. At a ap- 

 pear the aniheridia and 

 nt & the archegones on the 

 surface of the prothallns. 

 494, Antheridium. 495, 

 One nf its cells. 496, The 

 same burst ; and 497, the 

 sperm atozoid escaped. 

 These float about, and 

 some of them at length 

 enter. 498, the archcgone., 

 fertilizing, and at leneth 

 prodiicintr. 499. the young 

 Fern 50(1. Bonis of As- 

 pifliiim mnr<rinftle. covered 

 with the iurhifiium. 601, 

 Same, side view. 



