82 BOTANY 



and a number of fungi. The Thallophyta include also 

 the large fungi, the toadstools, and all the parasitic 

 and disease-producing forms mentioned in the pre- 

 ceding chapter. 



The Bryophyta form a much smaller group, reported 

 to have about sixteen thousand species. Some of these 

 appear, as do the mosses, to have true leaves, but their 

 apparent leaves are not really homologous with those 

 of the higher plants. They have some differentiation 

 of conducting cells in the tissue, but no true wood or 

 vessels. They have a definite alternation of genera- 

 tions, but the spore-producing generation grows on to 

 the a leafy " sexual generation, and is generally, but 

 wrongly, called its "fruit capsule." To this group 

 belong all the Mosses and Liverworts, and between them 

 and the rest of the cohorts there is one of the greatest 

 gaps in the whole plant world. We have no clue to 

 the course of their evolution, and no definite idea as 

 to their relation to the other groups. It is evident, 

 however, from their structure that they are less highly 

 organised than the succeeding group of the Pteridophyta. 

 This group, which makes so much more general impres- 

 sion on the landscape than does the preceding one, 

 does not include so many as five thousand species altc 

 gether. All its members have a well-marked differ- 

 entiation into leaves and stems, some with large leaves 

 like the Bracken fern and some with small leaves like 

 the Club-moss. All are provided with well-differenti- 

 ated wood and phloem, which are arranged in bundl % 

 in the stem, but none of the living forms have those 

 zones of secondarily formed wood which is character- 

 istic of the present higher plants and of the fossil pterido- 

 phytes. All the members, also, have a well-marked 

 alternation of generations, but it differs from that of 



