588 



THE FORMS OF TISSUES 



[CH. 



the point F'" (vertically under F), wbich tells us that the partition 

 now starts 45/100, or nearly halfway, along the radial wall. 



The foregoing considerations carry us a long way in our investi- 

 gation of the simpler forms of cell-division. Strictly speaking they 

 are hmited to the case of flattened cells, in which we can treat the 

 problem as though we were partitioning a plane surface. But it is 

 obvious that, though they do not teach us the whole conformation 

 of the partition which divides a more comphcated solid into two 

 halves, yet, even in such a case they so far enlighten us as to tell 

 us the appearance presented in one plane of the actual solid. And, 

 as this is all that we see in a microscopic section, it follows that 

 the results we have arrived at will help us greatly in the interpreta- 

 tion of microscopic appearances, even in comparatively complex 

 cases of cell-division. 



Let us now return to our quadrant cell (OAPB), which we have 

 found to be divided into a triangular and a quadrilateral portion, 

 as in Figs. 233 or 237 ; and let us _, 

 now suppose the whole system to 

 grow, in a uniform fashion, as a 

 prelude to further subdivision. The 

 whole quadrant, growing uniformly 

 (or with equal radial increments), 

 will still remain a quadrant, and it 

 is obvious, therefore, that for every 

 new increment of size, more will be 

 added to the margin of its triangular 

 portion than to the narrower margin 



of the quadrilateral; and the in- 



. Ml 1 • ^' ^ Fig- 237. 



crements will be m proportion to 



the angles of arc, viz. 55° 22' : 34° 38', or as 0-96 : 0-60, i.e. as 8 : 5. 



Accordingly, if we may assume (and the assumption is a very 



plausible one), that, just as the quadrant itself divided into two 



halves after it got to a certain size, so each of its two halves will 



reach the same size before again dividing, it is obvious that the 



triangular portion will be doubled in size, and therefore ready to 



divide, a considerable time before the quadrilateral part. To work 



out the problem in detail would lead us into troublesome mathe- 



