288 



SPOROPHYTE OF MARCHANTIA 



producing cells. This is an important departure from Riccio- 

 carpus and we see here the beginning of the tendency towards 

 the sterilization of sporogeneous cells that becomes more and 

 more pronounced in higher forms and that 

 plays [an important part in the evolution of 

 plant life. During the germination and growth 

 of the gametospore, a delicate membrane (the 

 perianth) grows up about the archegonium 

 and doubtless assists the involucre in pro- 

 tecting it against drying winds (Fig, 193, 

 p). When the spores are mature, the cells 

 of the stalk elongate, rupture the archego- 

 nium and push the capsule beyond the cur- 

 tains of the perianth and involucre, so that 

 it is exposed to the air (Fig. 195). The cap- 

 sule now ruptures, exposing the spores and 

 elaters to the air. The elaters, a word mean- 

 ing lifters, are very hygroscopic; they coil and 

 uncoil with the least change in the humidity 

 of the air and thus doubtless assist in the grad- 

 ual exposure of the spores to the air currents. 

 The spores germinate as in the lower liver- 

 worts. Thus we see that the sporophyte, 

 consisting of a foot, stem and capsule, is more 

 complex and larger than in Ricciocarpus. 

 This is doubtless due to the better nourish- 

 ment which it receives as a result of the de- 

 velopment of a more efficient absorbing organ, 

 the foot. 



105. Order b. Jungermaniales or Leafy 

 Hepatics. — By far the larger number of 

 hepatics belong to this order. They are 

 especially abundant in moist tropical countries, where they often 

 cover the stems and leaves with a rich vegetation, and with us 

 they are of common occurrence on dripping rocks and in deep 

 woods on the moist bark of trees and decaying logs or damp 

 earth. In the lower form the thallus is very simple and delicate 



Fig. 196. One of 

 simpler thalloid Jun- 

 germaniales, Pallavi- 

 cinia, showing the 

 rhizoidal growth on 

 the under surface of 

 the thallus and a 

 mature sporophyte 

 arising from a cup- 

 like perianth which 

 is surrounded at its 

 base with involu- 

 crate leaves.— H. O. 

 Hanson. 



