346 PRACTICAL BOTANY 



of elements essentially similar to those composing the 

 central bundle of the stem. 



2. In the sections of the upper part of the leaf note 

 that the arrangement of the tissues is for the most 

 part similar to that in the above sections, but rather 

 more bulky, while opposite each of the cells at the 

 upper surface is seen to be attached a series of three to 

 six chlorophyll-containing cells, which represent trans- 

 verse sections of those longitudinal plates or lamellae 

 above observed on the upper surface of the leaf, under 

 a low power ; the uppermost cell in each lamella (as 

 seen in section) is enlarged and forked. It is obvious 

 that these chlorophyll-containing lamellse are separate 

 laterally from one another : they constitute the chief 

 assimilating tissue of the plant. 



For comparison with the above, a Moss of simpler type may be 

 taken, e. g. Funaria hygrometrica. As before there is an erect stem, 

 with a mat of brown rhizoids at its base : it bears a number of 

 leaves of somewhat variable form, more or less widely ovato- 

 lanceolate. 



Mount a single leaf in water and examine under a low power : 

 note the clearly marked midrib, terminating in the acuminate 

 apex, the thin lateral portions, consisting of only a single layer 

 of cells containing chlorophyll, and bounded by an entire 

 margin. 



Cut transverse sections of the stem, and mount in weak 

 glycerine or glycerine jelly : on examination under a low power 

 it will be seen that the stem is of much simpler structure than that 

 of Polytrichum : the peripheral tissues have brown walls, but they 

 are not thickened to any marked degree : at the centre is a strand 

 of thin-walled, small-celled tissue : the peripheral tissues usually 

 contain chlorophyll. 



