144 H0FME1STER, ON 



nates, which is attached laterally to the margin of the leaf, 

 and consists of a longitudinal row of cells. These expand 

 downwards from the longitudinal axis of the leaf, and exactly 

 keep pace with the further multiplication of the cells from 

 which they sprang. As the increase in width of the leaf is 

 much less at the base than close above it, it follows that 

 in the perfect leaf the commissure of the two parallel cel- 

 lular surfaces appears to be considerably inclined sideways, 

 running obliquely from the margin of the leaf to the base 

 of the mid-rib. By the peculiar development of the bases 

 of the leaves, nature has more than sufficiently compensated 

 the youngest portions of Eissidens for the deficient protec- 

 tion which, owing to their mode of arrangement, the leaves 

 would be able to afford. 



^ When the young leaf of Eissidens has attained a length 

 of J-'", the multiplication of the apical cell terminates. At 

 this time the leaf retains the form which it had when in 

 a younger state; it is less slender than Avhen more fully 

 grown. The further multiplication of its cells is produced 

 exclusively by the continual division of those of its lower 

 portion. The great activity of this multiplication is shown 

 from the simple statement that the number of the cells of 

 the proportionally small point of attachment of the leaf, 

 when reckoned transversely, amounts to thirty. 



The six longitudinal rows of cells adjoining the median 

 line of the leaf of Eissidens become transformed into the 

 mid-rib, by division produced by septa parallel to the sur- 

 face of the leaf, and by the division of the newly formed 

 cells by septa perpendicular to the surface of the leaf. The 

 base of the mid-rib in the perfect leaf is immediately adja- 

 cent to the duplication of the lower part of the margin of 

 the leaf. 



The examination of half-developed leaves of mosses which 

 are undergoing this process of cell-multiplication will afford 

 one of the most convenient methods for the accurate inves- 

 tigation of the process of cell-division and the formation of 

 chlorophyll. The object is not large enough for the micro- 

 scopes of the present day. I believe, however, that I have 

 already made out some interesting peculiarities in Eissi- 

 dens. In the cells close to the base of the leaf the nucleus, 



