SYSTEMATIC BOTANY 88 



the bryophytes, for the leafy plant which is conspicuous 

 is the spore-producing generation, while the sexual 

 generation is a very small and inconspicuous little 

 structure, as simple as an alga except for its sexual 

 organs. To this cohort belong all the ferns, all the 

 Equisetums or Horsetails, and the Club-mosses and 

 Selaginellas. These three types of pteridophytcs are 

 separated into different phyla, for they differ in a 

 number of important respects, and their fossil repre- 

 sentatives add some further families to the group, but 

 they all agree in the essentials enumerated for the group 

 as a whole. In modern plants we have again a great 

 gap, and then come the Gymnosperms. This gap is 

 bridged by the fossil Pteridosperms. The gymnosperms 

 have all a well-marked differentiation into roots, stems, 

 and leaves, and all have differentiated wood and phloem. 

 Most of them grow to a considerable size, and have 

 strong, woody trunks with zones of secondary wood. 

 They all have complex fructifications with seeds, and in 

 most cases these are borne on special leaves or branches, 

 which often form a cone. The male cells are produced 

 in pollen which is borne by small separate cones. To 

 this group belong the Pine and Fir trees, the Yews, Cedars, 

 Larches, and the Spruce, as well as the sub-tropical and 

 comparatively rare Cycads. Of these there are not 

 more than a total of about five hundred species, though 

 in many districts, owing to their large size and their 

 numbers in the forests, they appear to be the most 

 important plants of the districts, as in the spruce forests 

 of Canada or the pine belt of the continental mountains. 

 The last and greatest group, the Angiosperms, with 

 over a hundred and thirty thousand species, contains 

 nearly all the plants that yield crops of economic im- 

 portance to man, or that decorate his gardens, or that 



