638 



THE FORMS OF TISSUES 



[CH. 



drical stalk, and dividing in accordance with its shape by means of 

 transverse septa. In all such cases the cells may continue to sub- 

 divide, and the manner in which they do so must depend upon 

 their own proportions; and in all cases there will sooner or later be 

 a tendency to the formation of perichnal walls, cutting off an 

 epidermal layer of cells, as Fig. 284 illustrates very well. 



The method of division by means of oblique partitions is a 

 common one in the case of "growing points"; for it evidently 

 includes all cases in which the act of cell-division does not lag far 

 behind that elongation which is determined by the specific rate of 



Fig. 283. Gemma 

 of moss. After 

 Campbell. 



Fig. 284. Development of antheridium 

 of Riccia. After Campbell. 



growth. And it is also obvious that, under a common type, there 

 must here be included a variety of cases which will, at first sight, 

 present a very different appearance one from another. For instance, 

 in Fig. 285 which represents a growing shoot of Selaginella, and 

 somewhat less diagrammatically in the young embryo of Junger- 

 mannia (Fig. 286), we have the appearance of an almost straight 

 vertical partition running up in the axis of the system, and the 

 primary cell-walls are set almost at right angles to it — almost 

 transversely, that is to say, to the outer walls and to the long axis 

 of the structure. We soon recognise, however, that the difference 

 is merely a difference of degree. The more remote the partitions 

 are, that is to say the greater the velocity of growth relatively to 



