32 Plant Life and Evolution 



veloped all the myriad forms of plant life that now 

 exist upon the earth. 



Are Ontogenetic Variations Inherited? Differ- 

 ent individuals of the same species in the course 

 of their development may be subject to very different 

 conditions, and these differences are reflected in the 

 change of form or in structural modifications that 

 are often very marked indeed. That such changes 

 arising in the course of ontogeny may assume 

 hereditary characters has not been positively proved, 

 but it is quite probable that where changed environ- 

 mental conditions exist for very long periods of 

 time, the ontogenetic structural changes might be 

 fixed, thus assuming hereditary value. Where, for 

 instance, plants from cold countries are grown in 

 milder ones, their habits may be much altered. 

 Trees which are deciduous in cold climates may hold 

 their leaves much longer or even assume an ever- 

 green habit when transferred to a warmer coun- 

 try. The time of flowering is also much influenced 

 by climate. For instance, in the mild, even tem- 

 perature of the coast region of California, many 

 garden flowers which in the Eastern States have 

 a marked seasonal growth and flower at a definite 

 time, may flower almost at any time of the year, 

 depending mainly upon the amount of water given 

 them, water being the principal factor in plant 

 growth in this region where it is never cold enough 

 to entirely stop growth. Many spring flowering 

 plants, such as the iris, primrose, violets, and many 



