REPRODUCTION AND SEX 459 



be that of the posterior end when that is liberated as a separate 

 worm. Behind this minimum hne, the metaboHc gradient rapidly 

 rises again, but soon falls towards the tail. There can be no doubt 

 that the physiology of reproduction must take account of areas 

 where the regulative control of other parts wanes away, and where 

 cells remain more free to assert their own individuality, even to 

 the establishment of a new grouping, if not even a new individual, 

 as often happens in Planarian and other simple worms. 



Returning to the growing axis of the flowering plant, the growing 

 point is the region with the highest rate of metaboUsm; and there 

 is a gradual decrease down the stem — a metaboUc gradient. Within 

 a variable distance from the growing point a controlling sway is 

 exerted over the incipient buds; they cannot develop until the tip 

 of the stem has grown to some distance away from them. If the 

 growing point is covered with a small cap of plaster of Paris, it 

 loses its physiological dominance, and the buds which were in- 

 hibited will begin to develop. If the plaster cap be removed, the 

 development of the buds will stop and the young shoots will die. 

 But if the lateral shoots developing from the buds had been able to 

 outstrip the apex of the stem before the cap was removed, then the 

 inhibition power of their growing points will predominate over that 

 of the apical shoot, which will therefore die. Here then is another 

 set of considerations to be kept in mind in trying to understand 

 reproduction. 



Anabolism and Katabolism. — But some attempt must be made 

 to find an intrinsic necessity for the alternation of the fundamental 

 processes of anabolic and katabolic preponderance. Multiplication 

 follows growth; reproduction see-saws with nutrition; what is the 

 fundamental reason for this ? Can we get below the general proposi- 

 tion that the more a material system accumulates potential energy, 

 the more liable it is to suffer loss — a tendency universal in the 

 physical world, but a tendency which living creatures have been 

 able in large and varying measure to evade. 



We ha\'e seen how the problem of this alternation, which is 

 of the essence of vital rhythms, has been discussed by Sager, who 

 believes that it is possible "to explain inherent rhythmicity as a 

 physicochemical consequence of the colloidal structure of proto- 

 plasm". The protein and other molecules built up in anabolism have 

 an architectural instability proportionate to their complexity. But 

 their breaking down, in which the potential energy of the edifice is 

 changed into the kinetic energy of what may be even a smashing 

 collapse, is happily restrained or resisted by the properties of the 

 viscous, emulsoid, colloidal protoplasm. The nature of this resistance 

 is beyond our scope here, but its effect is to make the discharge of 

 energy intermittent, and in alternation with the anabolic restoration 

 of the molecular architecture. Sager gives a picturesque illustration. 



