382 HOEMEISTER, ON 



stituting the edges of the spatula-like flat cellular mass, 

 the fore-edge of the latter soon appears deeply indented 

 (PL LIV, figs. 3, 5). Id one respect, however, even here 

 there is a preponderance of the development of one branch 

 of the fork ; the right or left fork, alternately, forms 

 a primary leaf* before its sister-shoot, even before the divi- 

 sion of the end of the stem is manifest. This leaf, there- 

 fore, appears to be situated on the middle of the underside 

 of the forking end of the stem (PL LIV, tigs. 5). By the 

 subsequent growth of the shoot it is pushed more on one 

 side. 



Each shoot of Selaginella is traversed in its upper portion 

 by two thin cylindrical woody bundles, whose position 

 corresponds with the foci of the ellipse represented by the 

 transverse section of the stem. Towards the base of the 

 shoot, near the points of junction with the other branch of 

 the fork, the two bundles unite to form one (PL LIV, fig. 3). 

 The differentiation of these vascular bundles from the 

 surrounding tissue of the stem first takes place in Selaginella 

 Galeottii underneath the second youngest pair of leaves. 

 The cells destined to form the vascular bundle lag behind 

 the neighbouring cells in transverse division, and divide 

 repeatedly by longitudinal septa radial to the axis of the 

 stem and parallel to it. This takes place even later in 

 8. hortensis, some time after the commencement of the 

 forking of the naked end of the shoot in question. In 

 this species the remarkably regular furcation of the vascular 

 bundle of each shoot f is manifestly in connexion with the 

 succession of the forkmgs of the stem. 



The cells immediately adjoining the vascular bundles 

 take no part in the remarkable longitudinal expansion of 

 the cells of the stem by which the leaves are removed far 

 from one another, and the first clear distinction between 

 stem and leaves is produced. The stretching of the neigh- 

 bouring cells of the bark and of the pith, as well as of the 

 vascular bundle itself, soon removes those cells from one 

 another, so that they have the appearance of proportionably 

 thin threads, which unite the vascular bundle which is 



* Teuille primaire, Spring. 



f See ' Kaulfuss Wesen der Famikrauter,' p. 25. 



