CELLULAR TISSUE 235 



comes to constitute that outer pellicle called epidermis both in animals 

 and plants. 



If then we study plants from the point of view of their internal 

 organisation, all that we can find is, among the simplest, a cellular 

 tissue without vessels but variously modified and stretched or com- 

 pressed according to the special shape of the plant ; and in the more 

 complex, an assemblage of cells and vascular tubes of various sizes, 

 mostly with lateral pores, and a varying number of fibres, resulting 

 from the compression and hardening that a portion of the vascular 

 tubes has undergone. This is all that the internal organisation of plants 

 presents, as regards their containing parts ; even their pith is no 

 exception. 



But if we study plants from the point of view of their external 

 organisation, the most general and essential points to observe are as 

 follows : 



1. Their various peculiarities of shape, colour and consistency, 

 both in them and their parts ; 



2. The bark which invests them, and gives communication by pores 

 with the environment ; 



3. The more or less complex organs which develop on the exterior 

 in the course of the plant's fife, and serve for reproduction ; they 

 perform their functions once only, and are highly important in the 

 determination of the characters and true affinities of each plant. 



It is then in the study of the external parts of plants, and especially 

 in that of their reproductive organs, that the means must be sought 

 for describing the characters of plants and determining their natural 

 affinities. 



Since the above exposition is a positive result of knowledge acquired 

 by observation, it is obvious that on the one hand the true affinities 

 among animals can only be determined by their internal organisation, 

 which provides the only features of real importance ; and that on the 

 other hand these affinities cannot be similarly determined among plants, 

 as regards any of the divisions which mark their classes, orders, families 

 and genera. In their case affinities can only be determined by a study 

 of their external organisation ; for their internal organisation is 

 insufficiently complex, and its various modifications too vague, to 

 provide the means for fulfilling this purpose. 



We have now seen that cellular tissue is the matrix, in which all 

 organisation was originally cast ; and that it was by means of the move- 

 ment of the internal fluids of li-\nng bodies that all their organs were 

 created in this matrix and out of its substance. We have now to 

 enquire briefly whether we are justified in attributing to nature the 

 power of forming direct generations. 



