THE HIGHER CRYPTOGAMIA. 363 



the winter the development of the leaves is considerably 

 retarded, but does not entirely cease. Those leaves which 

 are first formed in winter and make their appearance at the 

 end of the next autumn, are very imperfect. In the scanty 

 development of the leafy portion, and the vigorous develop- 

 ment of the base, they form the transition to the stipule-like 

 organ which in the terrestrial Isoetes, especially I. Durieid 

 and Hi/strix, appear at the commencement and the close of 

 every vegetative period.* In the semi-terrestrial species 

 such as /. velata and adsjiersa, the last leaves of the year 

 exhibit — in a more marked manner than I. lacustris — a dis- 

 torted leafy portion and an overgrown sheathing portion 

 whose cells are quite filled with starch and oil. 



The scales of the first leaves only of the germ-plant origi- 

 nate immediately above the place of attachment of the leaf. 

 With the second leaf frequently, with the third and following- 

 ones always, the case is different. Here the cell which by 

 the vesicular protrusion of its outer wall lays the foundation 

 of the scale, is removed by at least one cell from the base 

 of the leaf (PL XLYII, fig. 3; PL XLIX, fig. \ l ). The 

 intercalary cell-multiplication of the base of the leaf takes 

 place with remarkable activity in this one cell and in those 

 cells which lie in the same horizontal plane. By this means 

 the scale is carried upwards to some height on the leaf (PL 

 L, figs. 1, 2 ; PL LI1I, figs. 2, 3). A flat three-sided cellu- 

 lar mass then sprouts forth from, the leaf close under the 

 scale and covering the base of the latter (PL L11I, figs. 2, 3). 

 Beyond and over the sides of this cellular mass the two 

 lower angles of the triangular scale are developed in a down- 

 ward direction ; the base of the scale becomes heart-shaped 

 like the scales of the Polypodiaceee (PL XLIX, fig. 5). The 

 cells of the base, which are inserted in the tissue of the leaf, 

 exhibit a vitality which forms a marked contrast to the early 

 cessation of the growth of its free portion. The horizontal 

 row of cells produced by the multiplication of the first cell 

 of the second degree belonging to the scale — which cell is en- 

 closed by the substance of the leaf — is transformed by a 

 series of rapidly repeated divisions into a transversely-ex- 

 tended ellipsoidal cellular body, the two ends of which, by 



s Alex. Braun, in 'Exploration Scieutifique de l'Algerie,' PI. 36, fig. 1*, %. 



