208 



THE LIFE OF THE PLANT 



on the fact that both the elongation of the cells and their 

 division — the two phenomena which determine the 

 growth of organs as a whole — take place more energetic- 

 ally in the absence of light. But can we not find out the 

 approximate cause of this inhibitive effect of light ? 

 There are investigations which do to a certain extent 

 explain this phenomenon, and which at the same time 

 are connected with a question of great practical import- 

 ance. It was long ago known that stems grown in the 

 dark appear to be more watery and to have less tension 

 in their tissues. They are in general less turgid, as is 

 easily seen in cress grown in the light and in the 



Fig. 6o. 



dark. But a difference similar to that noticed in these 

 extreme cases {i.e. between stems grown in the light 

 and in total darkness) could be shown — to a smaller 

 degree, it is true — in plants grown respectively in the 

 shade and in a bright light. The suggestion has been 

 made that some such effect might explain the laying of 

 crops which, as we saw, people have vainly attempted 

 to explain by want of silicon (see chapter iv.). This 

 supposition might well have been based upon the fact 

 that for the most part it is cereals which are sown very 

 thickly that are badly laid, while this never happens 

 with thin crops, however strange it may seem at first 

 sight. The following method was used in order to 

 shade the plants of a crop artificially. One or more 

 plants were surrounded with a drain-pipe ; as soon as 



