350 DELATION TO ENVIRONMENT. 



essentially dilTcrent from early animal life. The simplest ones 

 which are clearl_\- recognized as plants are found among the 

 lower alg;e and fungi. These are single cells of very minute 

 size, roundish, oval, or oljlong, existing during their growing 

 period in water or in a very moist substratum or atmosf)here. 

 Examples are found in the red snow plant {Spharella 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 b_y food 

 material in solution. These food solutions are easily absorbed. 

 Becau.se of the minute size of the protoplasts and of the plant 

 bodv, thev do not have to soh'e problems of transport of food to 

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

 isms consisting of large numbers of j)rotoplasts closely com- 

 pacted together, the proljlem of relation to environment and of 

 food transport Ijecome felt; the larger the organism usualh' the 

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

 there is a gain bv a difTerentialion in the work of different proto- 

 plasts, some for absorption, some for '"oncluction, some for the 

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

 a gain in splitting the form of the plant hoA\ 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 bofly into parts, there are two general problems to 

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

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

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

 face to eii\ ironmcnt for (lie pur])ose of ac(|uiring food and the 

 disposition of waste, (j) The protection of the plant from 

 injuries incidcnl to an austere cn\'ironment. 



It is e\'idenl with llic great \arict\' of conditions met with in 

 different ])arts of the same localit)- or region, antl in different 

 parts of the glolie, that the plant has had \er\' complex problems 



