General Physiology of the Plant. 205 



cular plantb ui those parts where there are no vessels, as, for 

 example, in the cortex of the root, the parenchyma of grow- 

 ing parts, c. The turgid cells near the vessels, however, 

 give up some of their contents, which become squeezed into 

 the latter, more especially when the quantity of liquid in 

 plant is at a maximum, e.g. in spring. 



The extent of surface exposed by a plant by means of 

 its leaves is enormous, and from this evaporation of water 

 is constantly taking place. Since, however, the cells of the 

 leaves and neighbouring parts remain turgid, it follows 

 that the supply of water must be constantly renewed ; that, 

 in fact, the amount of water got rid of by transpiration must 

 be balanced by the amount absorbed ; and that in conse- 

 quence there must be a constant flow, at least during the 

 time when the leaves are out, from root to leaf. What is the 

 course of this regular circulation ? Numerous experiments 

 have proved that the water travels by the young wood of 

 the fibre-vascular strand, and by the substance of the cell- 

 walls, and not through the cavities, of the vessels save 

 under the conditions mentioned above. Trie amount of 

 water transpire! by the leaves varies of course with the 

 nature of the plant and of the atmospheric conditions, 

 according to laws which may easily be deduced. The 

 stomata have an important influence also on the amount tran- 

 spired. The rate of circulation of water in the stem is very 

 considerable, in some cases from 100 cm. to 150 cm. per hour. 



It has already been stated that the primary stages in 

 anabolism take place in the leaf, the result being the forma- 

 tion of, in the first instance, some comparatively simple 

 anastate such as formic aldehyde and then of some proteid. 

 Starch, the great reserve store compound, is also employed 

 as an anastate, though probably it is a product of the kata- 

 bolism of protoplasm in the first instance. In order that 

 the plant may be nourished a circulation of these substances 

 must take place. Since, however, starch and proteids are 

 practically insoluble it follows that they must be digested, or 



