35 RELATION TO ENVIRONMENT. 



essentially different from early animal life. The simplest ones 

 which are clearly recognized as plants are found among the 

 lower algae and fungi. These are single cells of very minute 

 size, roundish, oval, or oblong, ' existing during their growing 

 period in water or in a very moist substratum or atmosphere. 

 Examples are found in the red snow plant (Sphcerella nivalis), 

 the Pleurococcus, the bacteria; and among small colonies of 

 these simple organisms (Pandorina) or the thread-like forms 

 (Spirogyra, (Edogonium, etc.). It is evident that some of the 

 life relations of such very simple organisms are very easily ob- 

 tained that is, the adjustment to environment is not difficult. 

 All of the living substance is very closely surrounded by food 

 material in solution. These food solutions are easily absorbed. 

 Because of the minute size of the protoplasts and of the plant 

 body, they do not have to solve problems of transport of food to 

 distant parts of the body. When we pass to more bulky organ- 

 isms consisting of large numbers of protoplasts closely com- 

 pacted together, the problem of relation to environment and of 

 food transport become felt; the larger the organism usually the 

 greater are these problems. A point is soon reached at which 

 there is a gain by a differentiation in the work of different proto- 

 plasts, some for absorption, some for conduction, some for the 

 light relation, some for reproduction, and so on. There is also 

 a gain in splitting the form of the plant body up into parts so that 

 a larger surface is exposed to environment with an economy in 

 the amount of building material required. In this differentiation 

 of the plant body into parts, there are two general problems to 

 be solved, and the plant to be successful in its struggle for exist- 

 ence must control its development in such a way as to preserve 

 the balance between them, (i) A ready display of a large sur- 

 face to environment for the purpose of acquiring food and the 

 disposition of waste. (2) The protection of the plant from 

 injuries incident to an austere environment. 



It is evident with the great variety of conditions met with in 

 different parts of the same locality or region, and in different 

 parts of the globe, that the plant has had very complex problems 



