GROWTH AND SECRETIONS. 71 



continuing these processes : consequently, the 

 oxygen now acts in the same manner on the 

 living plant, as we find in experiment it acts upon 

 the dried green leaves, when moistened and ex- 

 posed to its action : they absorb gas and change 

 colour." (Researches on Light, p. 201.) 



To the fall of the leaf succeeds the dormant 

 wintry state : there is no absorption of moisture 

 from the air, except through the cellular en- 

 velope ; the roots have not yet formed the young 

 radicles, and are in their least active state ; and 

 on account of these concurring circumstances, 

 this is the most favourable period for trans- 

 planting. 



49. Cellular plants have, as has been said 

 before, no true vessels ; their fibres, if they may 

 be so called, are composed only of elongated 

 cells, and are never identical with the ligneous 

 fibre. The formation of the elongated cells, 

 when such exist, determines the direction of the 

 juices ; thus in the mosses, for instance, the stem 

 receives the water at its base, and by its radical 

 fibrils, and transmits it in a longitudinal direction 

 to the leaves, which direction is determined by 

 the elongated cells. These plants are likewise 

 nearly devoid of stomata, and can therefore only 

 exhale the superabundant water slowly, and 



