130 



STKUCTURAL BOTANY 



Here there are elements of various kinds. In the 

 middle, the large, central, rather thick- walled cells, which 

 may be of the nature of tracheides, and serve to con- 

 duct water, are accompanied by parenchyma containing 

 starch; outside this is a zone of smaller cells which have 

 more abundant protoplasm but no starch, and may 



fulfil the function of a 

 rudimentary phloem. In 

 this zone the sections of 

 leaf - trace bundles are 

 seen. 



The leaves of Funaria 

 are traversed by a con- 

 spicuous midrib, while 

 the rest of the leaf is 

 only one cell thick. The 

 cells of the thin part 

 are uniform, except at 

 the somewhat serrated 

 edge, where they are 

 narrower and have rather 

 thicker walls. The 

 midrib is several cells 

 thick, and contains a 

 small strand of narrow 

 cells, like those in the central cylinder of the stem. 

 Probably these cells conduct water and assimilated food, 

 while the function of assimilation belongs to the thin 

 part of the leaf, which is very rich in chlorophyll- 

 grains (Fig. 61, d). Moss leaves, by the bye, are very 

 favourable objects for observing the multiplication of the 

 chlorophyll-grains by division. 



The strand of conducting tissue enters the stem from 



FIG. 60. Transverse section of stem 

 of Atrichum undulatum, showing 

 central cylinder and adjacent tissue. 

 t, large water-conducting cells. The 

 finely dotted elements are the sup- 

 posed functional phloem. Among 

 these are small groups representing 

 leaf-trace bundles. The more ex- 

 ternal cells (containing starch- 

 granules) belong to the cortex. 

 Magnified 1 90. (After Haberlandt.) 



