134 PLANT-LIFE 



amination of the leaves shows that the blades are only 

 one cell thick, the cells being rich in chloroplasts ; but 

 the midribs are several cells thick, and include a strand 

 of narrow cells in the centre. This strand passes into 

 the cortex of the stem, but not into its central tissue. 

 Perhaps these narrow cells pass on assimilated food and 

 water. They seem to be the promise of a vascular 

 sytem of conducting tissue, which, however, can be 

 found fully developed only in higher plants. We shall 

 see it in the Ferns and their allies. The leaves of the 

 Mosses are evidently the principal carbon assimilators, 

 and they are by no means dependent upon the work of 

 the rhizoids for the absorption of water. The rhizoids 

 doubtless do absorb a great deal of water and the 

 needful mineral salts in solution, passing them upwards 

 to the parts of the plant where they are needed ; but the 

 leaves can, and do, absorb much water through the thin 

 walls of their cells. This being the case, an elaborate 

 conducting tissue is not needed. It is a matter of com- 

 mon observation that Mosses growing in exposed situa- 

 tions, where they are subject to periods of drought — as, 

 say, on a wall — seem to dry up and become lifeless in 

 dry weather; but after a spell of rain, they become as 

 green and vigorous as ever. They revive remarkably 

 quickly, the phenomenon being due to the ease with 

 which they can absorb water by means of their leaves. 

 The Moss-collector takes advantage of this capacity. 

 He knows that his specimens may be allowed to dry 

 and remain apparently withered for months, but they 

 recover freshness and form on being soaked in water. 



In higher plants, we note that lateral buds always 

 spring from the axils of the leaves — i.e., from the angles 



