190 THE STUDY OF ANIMAL LIFE CHAP, xi 



begins to divide after it has been penetrated, and in 

 some subtle way stimulated, by a male unit or sperm. 

 The great facts of individual history or development then 

 are, the apparent simplicity in the beginning, the pre- 

 liminary condition that the egg-cell be united with a male 

 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 very 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. It was a very impor- 

 tant step in the history of biology when Linnaeus, per- 

 ceiving the unity amid diversity, ranked animals and 

 plants together under the common title Organisata ; 

 and it was another great step when Claude Bernard, in 

 his Phenomenes de la Vie Communs aux Animaux et 

 aux Vegetaux (1878), made it clear that the two king- 

 doms of Organisata had, as regards their essential vital 

 processes, a great deal in common. 



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 diver- 

 gence and diversity are as undeniable as the inseparable 

 unity of the basal trunk and the genuine sameness of life 

 throughout the whole tree. Let us state the chief contrasts 

 between plants and animals in a tabulated summary : 



