TYPES OF CETPTOaAMS; BRYOPHYTES 283 



out of the center of which a younger portion of the stem seems to 

 proceed ; and this younger portion may in turn end in a similar 

 enlargement, from which a still younger part proceeds. 



Note the difference in general appearance between the leaves of 

 those plants which have just been removed from the moist collecting- 

 box and those which have been lying for half an hour on the table. 

 Study the leaves in both cases with the magnifying glass in order to 

 find out what has happened to them. Of what use to the plant is 

 this change ? Put some of the partially dried leaves in water, in a 



prim 



Fig. 207.— Protonema of a Moss. 



pHniy primary shoot ; h, a young root-hair ; pi, young moss-plant ; 

 6r, branches of primary shoot. 



cell on a microscope slide, cover, place under the lowest power of 

 the microscope, and examine at intervals of ten or fifteen minutes. 

 Finally sketch a single leaf. 



345. Minute Structure of the Leaf and Stem. — The cellular 

 structure of the pigeon-wheat moss is not }iearly as simple and con- 

 venient for microscopical study as is that of the smaller mosses, many 

 of which have leaves composed, over a large part of their surfaces, 

 of but a single layer of cells, as shown in Fig. 209. If any detailed 

 study of the structure of a moss is to be made, it will, therefore, be 

 better for the student to provide himself with specimens of almost 



