636 THE FORMS OF TISSUES [ch. 



each cell regulate the manner of its subdivision, that is to say the 

 form of the new cells into which it subdivides; or in other words, 

 the form of the growing organism regulates the form and number 

 of the cells which eventually constitute it. The complex cell- 

 network is not the cause but the result of the general configuration, 

 which latter has its essential cause in whatsoever physical and 

 chemical processes have led to a varying velocity of growth in one 

 direction as compared with another. 



In the annexed figure of an embryo of Sphagnum we see a mode 

 of development almost precisely corresponding to the hypothetical 

 case which we have just de'scribed — the case, 

 that is to say, where one of the four original 

 quadrants of the mother-cell is the chief 

 agent in future growth and development. 

 We see at the base of our first figure (a), 

 the three stationary, or undivided quadrants, 

 one of which has further slowly divided in 

 the stage b. The active quadrant has grown 

 quickly into a cyHndrical structure, which 

 inevitably divides, in the next place, into a 

 series of transverse partitions; and accord- 

 ingly, this mode of development carries with 

 it the presence of a single " apical cell," whose 

 lower wall is a spherical surface with its p^g ^gi. Development of 

 convexity downwards. Each cell of the Sphagnum. After Camp- 

 subdivided cylinder now appears as a more ^^^• 

 or less flattened disc, whose mode of further subdivision we may 

 prognosticate according to our former investigation, to which subject 

 we shall presently return. 



(2) In the next place, still keeping to the case where only one 

 of the original quadrant-cells continues to grow and develop, let us 

 suppose that this growing cell falls to be divided when by growth 

 it has become just a little greater than a hemisphere; it will then 

 divide, as in Fig. 282, 2, by an oblique partition, in the usual way, 

 whose precise position and inclination to the base will depend 

 entirely on the configuration of the cell itself, save only, of course, 

 that we may have also to take into account the possibility of the 

 division being into two unequal halves. By our hypothesis, the 



