6 PKACTICAL 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 

 five 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. It is now obvious that these chlorophyll- 

 containing lamellae 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 Jiygrometrica. 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. 



Gut 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. 



Sexual Organs. 



VI. Take a mature antheridium-bearing axis of 

 Polytrichum, and dissect it with needles in a watch- 



