THE SELECTION OF PLANT TYPES. 199 



preserved by pressing the leaves on which they grow or by 

 placing them in alcohol. The large and simply formed conidia 

 are developed in midsummer, while the primitive, readily under- 

 stood sexual fructifications follow in early autumn. They serve 

 to show the salient features of the Ascomycetous group, com- 

 parable in its reproduction with the red Algae, and they illus- 

 trate clearly the important phenomena of parasitism, showing 

 the haustoria by which the cells of the host plant are robbed of 

 their contents. 



8. Agaricus, the mushroom, obtainable at any time in the 

 city markets and readily preserved in alcohol, has a highly 

 specialized fructification, representing the culmination of one 

 of the lines of development in the great non-sexual Basidio- 

 mycetous group. The building up of a structure so highly 

 differentiated externally from simple filamentous elements is 

 instructive. If time permits, it is of interest to examine a 

 lichen, at least sufficiently to show it to be composed of a fun- 

 gus, commonly ascomycetous, and an alga living in intimate 

 and peculiar association. 



As we pass to the higher plants, the comparative similarity 

 in the life history of the members of each great group makes a 

 single type do much broader service. The development of the 

 Bryophytes is, in its essentials, so uniform that a single example 

 may serve to illustrate it. 



9. Pellia or Pallamcinia, or a similar thallose liverwort, 

 seems to me, on the whole, best suited to the purpose. From 

 the study of almost any Bryophyte the idea of the alternation 

 of generations may be readily gained, but the comparison of 

 the simple thallus of Pellia with the prothallus of the Fern 

 is instructive; while its relation to the leafy mosses is less 

 important, since these represent a side shoot from the main 

 line of plant development. The simple sporogonium of the 

 Hepatics is also much more typical than the complicated moss 

 capsule. The most familiar Bryophyte type for this use prob- 

 ably owes its selection to its very common occurrence in some 

 localities, but a member of the group less adapted to the pur- 

 pose could hardly be named than this Marchantia. Its massive 

 thallus is very highly specialized and of a structure peculiar to 



