364 HOFMEISTElt, ON 



repeated multiplication of the cells, ultimately grow upwards 

 in such a manner that the base of the scale becomes a fleshy 

 mass of very small cells with turbid contents, having the 

 form of a horse-shoe opening upwards, and inclined inwards 

 to- the longitudinal axis of the leaf. Underneath also the 

 exuberant growth of the base of the scale extends into the 

 three-sided shoot of the front surface of the leaf, partly 

 pushing forward the existing cellular tissue (PL LIII, fig. 5). 

 As the longitudinal development of the leaf draws to a close, 

 those of its cells which adjoin the highly-developed base of 

 the scale become ligneous by spiral thickenings of the walls. 

 Almost all the cells of the interior of the ligule-like shoot of 

 the fore-side of the leaf take part in this wood-formation* 

 (PL XLIX, fig. 1). In an upward direction it is only the 

 one cellular layer adjoining the place of insertion of the 

 scale which is transformed into spiral cells ; on the other 

 hand the whole of the tissue enclosed by the two horns of 

 the half-moon-shaped base of the scale becomes woody. 

 The middle of the lower end of the woody mass- which is 

 produced at a late period reaches close to the axile vascular 

 bundle of the leaf. 



The leaves of Isoetes lacustris which are formed in the 

 third year after germination, and are developed in the 

 fourth year, produce the first fruit. The rudiment of the 

 sporangium f is formed in the earliest youth of the leaf, at 

 the time of the commencement of the intercalary multipli- 

 cation of its base. Of the two cells into which — by a 

 tranverse septum — the cell underneath the place of inser- 

 tion of the scale is divided, the upper one becomes the 



* First observed by Mettenius, ' Linngea/ 1S4-7. 



f Schleiden, out of love for some supposed analogies with the lower crypto- 

 gams, will only apply the term " sporangia " to the spore-mother-cells of the 

 mosses and vascular cryptogams. Like most other botanists, I use the term 

 "sporangia" for the fruit containing the spore-mother-cells and spores, for 

 the capsules of mosses and liverworts, for the fruit of ferns aud Lycopods, and 

 for those portions of the fructification of the Equisetace* and Khizocarpese 

 which immediately enclose the spores. I do so because the term " sporangium" 

 was first applied to the fruit of ferns. It appears neither necessary nor advisa- 

 ble to use the same term for the Fungi, Lichens, and Alga?, as is used for the 

 Characeee, mosses and vascular cryptogams. Moreover the expression " spo- 

 rangium " is quite unnecessary in the case of the lower cryptogams. De- 

 scriptive botauy already possesses a more than sufficient number of suitable 

 names for the organs iu Question, 



