How Plants Resist Hostile Forces Around Them 257 



great powers of reproduction and growth, plants live in a world 

 already quite filled, and are therefore exposed to a competitive 

 struggle with one another, of which natural selection is the re- 

 morseless arbiter, and a survival of the fittest the inevitable 

 outcome. In a word, plants live in a world that is generally 

 friendly, but sometimes is hostile even to a mortal degree. 

 Against the hostile features of the environment they have had 

 to develop protective adaptations, some of which are extremely 

 conspicuous and play a large part in the determination of the 

 habits and aspects of plants. These protective adaptations, of 

 course, must co-exist and compromise with those physiological 

 adaptations in leaf, stem, and root, which we have already con- 

 sidered. The identification, separation, and definition . of the 

 structures and features of plants which are protective is the task 

 that now lies before us. 



To begin with, the protoplasm of plants is physically weak, 

 but secures an efficient first line of defense by the most obvious 

 of all methods, viz., through encasing each one of the soft-bodied 

 cells in a separate coating of armor, the cell-wall. As the 

 reader will recall, from the description in the chapter on Proto- 

 plasm, the plant skeleton is constructed from the united wall- 

 mass of the cells; and it thus combines both support and seclu- 

 sion for the protoplasm in its cavities, very much as the walls of 

 our many-storied houses do for us. Such a combination of skele- 

 ton and protecting wall is permitted only by the sedentary habits 

 of plants, and stands in very great contrast with animals, whose 

 locomotive habit requires a jointed skeleton, moved by masses 

 of contractile, and therefore naked (muscular) cells. 



Turning now in detail to the various hostile influences against 

 which plants need protective adaptations, the most obvious is 

 that of the winds, which, however, become a danger only as they 

 rise into gales. Then, as all will agree who have seen a great 

 tree tossed in the grasp of a tempest, protection is found in the 

 slenderness and elasticity of the branches, which yield in great 



