344 PRACTICAL COURSE IN BOTANY 



and chlorophyll so that it is capable of manufacturing food. 

 In this respect it shows a distinct advance on the correspond- 

 ing phase of the liverworts — if we except the single genus 

 Anthoceros, which alone among the liverworts has the cells 

 of the sporogonium i)r()vided with chlorophyll. 



400. Alternation of generations. — The process of repro- 

 duction in mosses is so closely similar to that of liverworts 

 that it is unnecessary to repeat the details. There are 

 some minor variations, but in all essentials the processes 

 are the same and may be represented to the eye by the 

 same formula. 



401. Relative position of mosses and liverworts in the 

 line of evolution. — Though mosses, as a rule, show a higher 

 degree of organization than liverworts, in both generations, 

 their development has been away from the general course 

 of evolution followed by the higher plants. This, as will 

 be seen later, tends towards a decreasing complexity of 

 the gametophyte with increasing complexity of the sporo- 

 phyte, while the mosses show increasing complexity of both. 

 Like the order of birds in the animal kingdom, they form 

 a highly specialized and somewhat isolated group. AMiile 

 they may be regarded as descendants from a common an- 

 cestral stock with the ferns and club mosses, they have 

 been switched off, so to speak, on a side track of the great 

 evolutionary trunk line, and their advance on this side 

 track has carried them to a point more remote from the 

 course along which the higher forms of plant life have 

 traveled than the distant junction at which they branched 

 off from their less progressive kindred, the humble liver- 

 worts. 



VII. FERN PLANTS 



Material. — Any kind of fern in the fruiting stage. Several different 

 varieties should be cultivated in the schoolroom for observation. While 

 gathering specimens, look along the ground under the fronds, or in green- 

 houses where ferns are cultivated, among the pots and on the floor, for 

 a small, heart-shaped body like that represented in Figs. 501, 502, called 

 a prothallium. It is found only in moist and shady places, and care should 



