92 



HOFMEISTER, ON 



multiplication of the cells of the second degree belong- 

 ing to the upper surface, than in those which are pro- 

 duced by the multiplication of the like cells of the under 

 surface. The increase in the number of cells, in the direc- 

 tion of the thickness, from the apex of the young shoot 

 backwards, is not unfrequently so rapid that the profile of 

 the shoot appears like a very slightly pointed triangle 

 (PI. XIII, fig. 11). The continual increase of the breadth 

 of the young shoot during its longitudinal growth takes 

 place by the division of the lateral cells of the fore edge by 

 means of longitudinal septa parallel to the longitudinal 

 axis of the shoot (PI. XIII, fig. 4). In a more advanced 

 stage of growth, the cells lying nearer the middle of the 

 fore edge also divide by longitudinal septa, slightly diverg- 

 ing from the direction of the median line. The shoot 

 then exhibits a middle row of cells, from which the other 

 cells diverge right and left at different altitudes, like the 

 rays of a fan. The earliest rudiment of each shoot is 

 a simple cell, having a trapezoidal basal outline, situated 

 in the axil of two older shoots (PL XIII, fig. 4, a) ; at 

 a little later period many such cells lying near one another 

 are found, in consequence of the commencement of the 

 longitudinal growth, to be already several times transversely 

 divided by inclined septa (PI. XIII, fig. 4, b). The 

 shoot, as it becomes developed, springs forth in the form 

 of a short projection, having its cells arranged in the order 

 already described, from the axil formed by the two older 

 adjoining shoots. 



The under side of each joint of the stem of Riccia glauca 

 exhibits on each side of the median line small, distichous, 

 obliquely attached leaves, formed of a simple layer of deli- 

 cate, transparent, cellular tissue (PI. XIII, fig. 3). They 

 resemble in all their parts those of the Marchantise, and, 

 like the latter, are for the most part rapidly destroyed by the 

 bursting forth of hair-like roots. The hollows of the old 

 roots of Riccia, like those of the Marchantiae, are furnished 

 upon the inner side with very numerous little points pro- 

 jecting inwards (PI. XIII, fig 4 J ). 



On stem-joints which have a tendency to form fruit, in- 

 dividual cells of the upper surface, situated in the angles 

 of the lateral and of the median shoots, protrude out- 



