Chap, n.] OF GROWTH IN THE VEGETAL KINGDOM. 278 



with the complex phanerogamous plants. There the faoulty of 

 self-multiplication by division is in some degree the special 

 appanage of incompletely developed cells, always young. These 

 are the cells which issue from the mother cells, which diversify 

 themselves and form the different histological vegetal types, of 

 which we have before given- a succinct account. Fi-om them 

 issue the tubes, the ligneous cells, the chlorophyllian ceUs ; but 

 all these derived and. special elements have, on the other 

 hand, habitually lost the faculty of division and of multi- 

 plication. 



Growth is only an exaggeration, an outcome of nutrition ; that 

 is to say, it is dependent upon the grand conditions of the 

 medium which, regulate this primordial pi-operty of organized 

 matter. 



Nevertheless, it appears only to depend indirectly upon light. 

 In efiect, it is often in the night, that seem to go on most strongly 

 the growth and segmentation of the vegetal cells. The necessary 

 conditions are simply the previous existence, in the tissues of 

 the plant, of a store of materials, elaborated, assimilable, and 

 of a sufficient quantity of aqueous vehicle to dUute and convey 

 these materials. 



The action of light on the chlorophyll . is necessary to the 

 formation of the immediate" assimilable principles in the plant ; 

 but assimilation, properly so called, is carried on very well' in 

 darkness. In efiect, the subterranean parts of plants live and 

 develop themselves ; the phenomena of germination are perfectly 

 accomplished in darkness ; truffles and all tuberaceous plants 

 effect subterraneously all the phenomena of their development j 

 mushrooms, deprived of chlorophyll, assimiTate even when the 

 organic materials are prepared by other organized beings. 



Light seems even to retard the development of the plant. It 

 is in the morning, towards sunrise, that the internode in its 

 process of growth offers its maximum of horary augmentation. 

 If a stem receives upon different sides of its sm-face luminous 

 rays varying in intensity, it curves itself towards the side on 



