140 



PLANT RELATIONS. 



if necessary, the parts of the leaf or the stem itself twisting 

 to allow the blade to assume this position. The danger of 

 the leaves shading one another is reduced to a minimum by 

 the elongation of internodes, the spiral arrangement, short- 

 ening and changing direction upwards, or lobing. 



This outlines the general nutritive relations, the roots 



Fig. 143a. Germination of the garden bean, showing the arch of the seedling stem 

 above ground, its pull on the seed to extricate the cotyledons and plumule, and 

 the final straightening of the stem and expansion of the young leaves.— After 

 Atkinson. 



and leaves being favorably placed for absorption, and the 

 latter also favorably placed for photosynthesis. It is im- 

 portant to study the behavior of various plants in the 

 germination of the seed, for in a comparatively short period 

 all of the important external relations of the vegetative 

 organs are established. Seeds should be selected that ger- 

 minate rapidly, and that represent different great groups, 

 such as squash, bean, corn, etc., and these observations 

 should be extended as far as possible by including the obser- 

 vation of seedlings in nature. 



