370 



HOW CROPS GROW. 



5. 



DIRECTION OF VEGETABLE GROWTH. 



One of the most obvious peculiarities of vegetation is 

 that the roots and stems of plants manifest more or less 

 regular and often opposite directions of growth. Roots, 

 in general, grow downwards; stems, in general, upwards, 

 though this is by no means a universal rule, both roots 

 and stems oftentimes manifesting either tendency in dif 

 ferent points or at different times of their growth. 



Sachs describes the following mode of observing the 

 directive tendency of root and stem. 



E, fig. 71, is a glass flask containing some water; it is 



closed above by a cork from 



which a young seedling is 

 suspended by means of a 

 wire. The flask stands upon 

 a plate of sand, and it is 

 shielded from the light by a 

 paste-board cover, .72, the 

 lower edge of which is forced 

 down into the sand. The 

 water in the flask keeps the 

 enclosed air in a moist 

 state. In the experiment, a 

 sprouted nasturtium seed 

 (Tropceolum majus) having 

 a perfectly straight descend 

 ing radicle, was placed at 

 night in the apparatus with 



the radicle pointing upwards 



Fig. 71. 



and the plumule downwards. The next morning the 

 seedling had the appearance of the figure. During the 

 night the tip of the root curved over and the plumule 

 sensibly raised itself. By continuing a similar experiment 



