102 



Elementary Biology. 



of differentiation, for we find in it still further developed the 

 different systems of tissues foreshadowed in the stem of 

 Fucus (fig. 32). Superficially, the cells have their walls 



FIG.3X.-/W,***,* thickened > and of a dark er colour (yellow 

 commune, TERMINA- or brown). The cells forming the cortical 



TION OF THE FEMALE . . . . . , 



PLANT. (Maoutand tissue have also thickened cell-walls, but 

 becoming thin-walled as they approach 

 the centre. Such cells of tolerably uniform 

 diameter and imdifferentiated character 

 receive the name of parenchymaj or 

 parenchymatous tissue. The central 

 cells of the stem differ in character in 

 different species of moss. In the type 

 chosen for consideration the cells are 

 elongated and thick walled, forming a 

 tolerably firm axis or support, to which 

 the name of sclerenchyma or sclerenchy- 

 matous tissue is given. In higher plants 

 there is found running through the stem, 

 branches, roots, and leaves, a very perfect 

 system of strands of sclerenchyma accom- 

 panied by vessels and variously modified 

 cells, of which we shall have to speak 

 afterwards more in detail. That system 

 has been called the fibre-vascular system. 

 One is at first inclined to look upon this 

 axial strand in the moss stem as a rudi- 

 mentary fibro-vascular strand. It is 

 scarcely correct, however, to adopt that 

 view, seeing that the moss plant and the 

 ordinary flowering plant are not compar- 

 able organisms in fact, as we shall after- 

 wards see, do not belong to the same 

 generation. Even the terms stem, leaf, root, are used to 

 indicate structures, at the most, only analogous to the corre- 

 sponding parts in higher plants. Only a few species of moss 



