THE LIVING SUBSTANCE. 143 



(j) In the plant kingdom, the extra hoards of internal con- 

 ditions become more rigidly adjusted to known rhythms of 

 supply so that, as a rule, plant individuals are more readily and 

 radically damaged by sudden environmental adversity than the 

 animal units are apt to be, the habits of the latter being adjusted 

 to meet intermittence in habitual sources of supply. 

 . It has been impossible because of rigidly limited space, to 

 do more than indicate in this section the leading lines of argu- 

 ment, and grouping of facts which have offered the standpoint 

 discussed. Here too, as throughout the article, I have preferred 

 to use as evidence so far as possible phenomena observed per- 

 sonally, although there are innumerable established facts which 

 might be cited, and the reader will, it is thought, find in his 

 own mind stores of added confirmation. 



[141] To sum up in a few words the gist of what I have 

 striven to make clear : The living substance down to its final 

 visible subdivisions is seen everywhere seeking or selecting its 

 own environment. All its guises and aspects, all its phases 

 and phenomena are to this end ; and chiefly that the perpetua- 

 tion areas shall be supplied with such environmental substances 

 as will render them for long periods independent of the chances 

 of external environment and then leave them prepared to resume 

 the struggle for other similar areas in turn. 



[142] That so potent and radical a function of the substance 

 should have areas of differentiation devoted to it, that it should 

 have given rise to substance organs, or centres of such control, 

 would seem a most natural thing. I believe that such organs 

 were, indeed, among the earliest formed of all areas of differ- 

 entiation, — excepting simple ectosarc. They are distributed 

 through all living masses at short intervals, the first care of 

 the substance in increasing its mass to any extent, or in in- 

 creasing its scheme of areal differentiation, seeming to be to 

 secure repetitions of just such centres of control or substance 

 organs, and the surrounding substance in many cases, perhaps 

 in most, seems to have lost the power to do without them, — 

 just as a mammal has lost the power to do without its heart or 

 lungs. I refer of course to the nuclei. Up to the present 

 time there is ever-increasing evidence that they may rightly be 



