28 IIOFMEISTER, ON 



similar slice from a Meniscus. Through the division of these 

 cells by means of septa parallel to the surfaces of the plant, 

 the shoot increases in thickness. The first of these septa does 

 not coincide with the ideal axis of the shoot ; the two parts 

 into which it divides the cell are very unequal (PI. IV, fio-. 

 25). The two newly formed cells divide again several times 

 by horizontal septa ; the thickness of the plant, however, 

 never seems to go beyond eight layers of cells. From some of 

 the cells near the fore edge, hairs, shaped like a club, and 

 bent forwards, take their origin. The latter become bicellu- 

 lar, soon after their appearance, by the growth of a transverse 

 septum. The basal cell, when fully grown, usually con- 

 tains starch-granules ; the terminal one, a thin fluid muci- 

 lage. A membranous layer of tough gelatine encloses 

 the growing fore edge of these hairs. The cells which form 

 the permanent upper and under surface of Pellia ultimately 

 divide by a vertical, longitudinal, and transverse septum ; 

 so that each cell of the outer layer is four times as small as 

 one of the neighbouring inner cells. This division occurs 

 sometimes in the fourth youngest, sometimes even in the 

 seventh youngest group of cells produced by a cell of the 

 second order. As the growth of a shoot progresses, the 

 activity of the cell-multiplication in the direction of its 

 thickness diminishes continually from the base to the fore 

 edge, more slowly, however, in the median line than at the 

 sides. The free margin of each shoot of which the deve- 

 lopment is completed, is formed of a single layer of cells ; at 

 the base of the indentations of this margin are found pro- 

 tuberances of cellular tissue projecting downwards : these 

 are the young new shoots. 



The shoots of barren plants growing in flowing water 

 exhibit conditions in the position and shape of their cells, 

 which can only be explained by looking upon them as forms 

 transitional between the first and the second form of cell- 

 multiplication (PI. IV, figs. 26, 27). 



It is a remarkable circumstance that, in the earliest 

 spring-shoots of Pellia, the two sides, owing to the more 

 vigorous expansion of the cells of one of them, are always 

 unequally developed. One of the shoots which protrude 

 themselves from the indentations of the fore edge pushes 



