380 HOFMEISTER, ON 



of Selaginella Martensi. The papilla assumes a conical form. 

 The sharp apex of these unicellular hairs, which represent 

 the teeth of the margin of the leaf, are soon entirely filled 

 by rapid thickening of the walls. The conical mass of cel- 

 lulose often bears a deceptive resemblance to a small cell, 

 owing to the seam of light which its edges exhibit when 

 seen with transmitted light (PL LVI, fig. 7). The two 

 rows of cells of the upper side of the leaf which immediately 

 adjoin the marginal cells, exhibit in many species definite 

 appendages of the outer wall. For instance, S. Galeottii 

 has two longitudinal rows of bluntish warts, similar to those 

 on the outer side of the hairs of many Boraginese (PI. LVI, 



Numerous chlorophyll-granules are formed in the narrow 

 cells of the upper surface of the leaf In S. Galeottii and 

 Martensi they have a distinctly vesicular appearance, and 

 contain some very small starch granules. In the square 

 cells of the underside of the leaf the green mucilage 

 coagulates into a single large spherical ball, as is the case 

 in Anthoceros (PL LVI, fig. 8). At the places where the 

 cells of the under-surface of the leaf adjoin those of the 

 upper, a connected net-work of air-cavities is produced by 

 the parting asunder of the edges of contact of the cells of 

 the under side from the closely connected cells of the upper 

 side of the leaf. The place of contact of each cell of the 

 under surface of the leaf with the cells of the upper surface 

 is surrounded by an air-cavity which is usually six-sided. 

 Towards the outside the cells of the under-side of the leaf 

 are in close connexion. 



The Lycopodiacese in general, and especially the 

 species of Selaginella, whose stems are elliptical in a trans- 

 verse section, afford some of the most marked instances of 

 true forking of the apex of the stem, which are to be found 

 in the whole of the vegetable kingdom. In all species 

 of Selaginella, whose leaves have the 2\ arrangement, 

 a forking of the stem occurs, almost without excep- 

 tion,* after each four circuits of leaves ; and the same 

 thing occurs also in those species whose shoots are appa- 

 rently quite simple and undivided for a considerable dis- 



* The only exceptions I know are seen now and then in S. helvetica. 



