VIIl] 



OR CELL-AGGREGATES 



405 



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 division, the less abrupt will be the 

 alternate kinks or curvatures of the portions which lie in the 

 neighbourhood of the axis, and the more will these portions 

 appear to constitute a single unbroken wall. 



(3) But an appearance nearly, if not quite, indistinguishable 

 from this may be got in another way, namely, when the original 

 growing cell is so nearly hemispherical that it is actually divided 

 by a vertical partition, into two quadrants ; and from this vertical 

 partition, as it elongates, lateral partition- walls will arise on either 

 side. And by the tensions exercised by these, the vertical partition 

 will be bent into little portions set at 120° one to another, and the 



Fig, 189. 



whole will come to look just like that which, in the former case, 

 was made up of portions of many successive obHque partitions. 



Let us now, in one or two cases, follow out a httle further the 

 stages of cell-division whose beginning we have studied in the last 

 paragraphs. In the antheridium of Riccia, after the successive 

 oblique partitions have produced the longitudinal series of cells 

 shewn in Fig. 186, it is plain that the next partitions will arise 

 periclinally, that is to say parallel to the outer wall, which in 

 this particular case represents the short axis of the oblong cells. 

 The effect is at once to produce an epidermal layer, whose cells 

 will tend to subdivide further by means of partitions perpendicular 

 to the free surface, that is to say crossing the flattened cells by 

 their shortest diameter. The inner mass, beneath the epidermis, 

 consists of cells which are still more or less oblong, or which become 



