In Plants and Animals. 77 



Nor do these traces of unity become more shadowy 

 when they are looked into more steadfastly. 



The conclusion arrived at in the last chapter was that 

 nerve and muscle and vessel and bone and other special 

 structures appear as layers in the walls of a hollow sphere 

 or cell, and that subsequently these layers are transformed 

 into rings or zones by opening out at opposite poles. 

 The course of development in this case, that is to say, 

 is from the cell, first towards lamination, and then 

 towards zonulation. Nor is it otherwise in the plant. 

 In the rounded and hollow peach there is a distinct 

 separation into layers of which that which forms the 

 stone may be rightly regarded as homologous with the 

 bony layer in the eye of the eagle of that layer which 

 elsewhere may become the vertebral ring : and the state 

 of things which is met with here is substantially that 

 which is met with in the husks of seeds, in the walls of 

 the nodes of the stem and branches, and in many other 

 parts of the plant. There is ever at work a " law of 

 compensation " by virtue of which any over-development 

 of one layer is at the expense of one or more of the 

 others. Usually the woody layer is the only layer which 

 is developed very conspicuously : always, however, there 

 are traces of soft layers, and in many succulent fruits 

 these are in excess of the hard layer. In some cases, 

 too, as in the leaves of the sensitive plant, and Dioncea 

 muscipula, certain parts probably altered axillary buds 

 in the first case approximate closely to the " irritable " 

 textures of animal bodies in their characters. Nor are 

 traces of zonulation wanting in plants. One such trace 

 is found in the case where several cells unite so as to 

 form a vessel with a continuous cavity, for here each 

 cell becomes more or less zonular by opening out in 

 opposite directions. Another such trace is found in the 



