TYPES OF CRYPTOGAMS; 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 
FiaG. 207. — Protonema of a Moss. 
prim, primary shoot ; h, a young root-hair ; pl, young moss-plant ; 
br, 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 nearly 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 
