14 PLANT SUCCESSION AND CROP PRODUCTION 



So with plant ecology, the earliest concepts of plant associations 

 have become enlarged and more flexible as it was found necessary 

 to make them more inclusive. The first ecologists perceived a rela- 

 tion of certain plants to dry situations and certain others to moist 

 ones — a most natural sort of grouping. Theophrastus (B. C. 370- 

 286) recognized this in the following words: "All (plants) are dis- 

 tinguishable as either terrestrial or aquatic, just as we primarily 

 distinguish animals; for there are some plants which grow no- 

 where but in the sea ; others affect only marshes or other very wet 

 places. Some cannot live in wet ground, but restrict themselves to 

 dry ground. Certain others are littoral only. A few trees thrive 

 in either moist land or dry, such are the myrtle, alder, and willow." 

 Except for the implication that plants are endowed with will by 

 the use of the word "restrict," this sounds fully as modern as any 

 ecological remarks could be which have been written without the 

 inspiration of the point of view of succession. 



Plant succession has progressed in making an ecological classi- 

 fication understandable, because it consists essentially in a genetic 

 conception of vegetation. As the name indicates, succession is the 

 sequence of plant associations which dominate a locality as the de- 

 velopment of the vegetations proceeds. In the sequence each stage 

 is made possible because of the next or remote preceding stages. As 

 the term genetic suggests, one stage in the development grows out 

 of the preceding stages. A habitat then does not so much consist in 

 rocks or hills or lake, as it does in so much moisture, so many de- 

 grees of heat, such an amount and quality of light. A habitat is 

 not viewed dynamically until it is placed on a strictly factorial basis. 

 The field worker sees plants growing in sand along the seashore. 

 He must think of them in terms of the water balance of the plant, 

 the abundance of light, temperature, and so fortth. 



Obviously, the ecologist does not attempt to control the condi- 

 tions of plant growth and vary them one at a time as one might 

 in a laboratory. The best that he can hope to do is to measure and 

 record the conditions he sees as carefully as his needs require. He 

 may even prove that succession is taking place by photographs 

 made at different intervals. The complete series of stages in most 

 successions are far beyond the space of an individual's life so his 

 records must be capable of interpretation by his successors. But 

 it is not necessary to see a complete succession in one place. One 

 may piece together the whole fascinating story of succession from 



