CHAP. XI The Elements of Structure 169 



unit, and the mode of growth by repeated division of the 

 ovum and its daughter-cells. In those plants with which 

 we are most familiar, the facts seem different, for we watch 

 bean and oak growing from seeds which, instead of being 

 simple units, are veiy complex structures. But the seed is 

 not the beginning of a plant, it has already a long history 

 behind it, and when that history is traced back to the seed- 

 box and possible seeds of the parent plant, there it will be 

 seen that the beginning of the future herb or tree is a single 

 cell. This is the equivalent of the animal ovum, and, like 

 it, begins its course of repeated divisions after it has been 

 joined by a kernel or nucleus from the pollen grain. 



Thus, to sum up, along three different paths we reach 

 the same conclusion, that there is a fundamental unity 

 between plants and animals. In the essential activities 

 of their life, in the stones and mortar of their structure, 

 and lastly, in the way in which each individual begins and 

 grows, there is a real unity. 



Yet, after all, plants and animals are very different. 

 The two kinds of organisms may be ranked as two great 

 branches of one tree of life, yet the branches diverge 

 widely and bear different foliage. The facts of divergence 

 and diversity are as undeniable as the inseparable unity of 

 the basal trunk and the genuine sameness of life throughout 

 the whole tree. I have stated the chief contrasts between 

 plants and animals in a tabulated summary — 



