244 H0FME1STEII, ON 



stipes. They originate here from the vascular bundles 

 which run on the hind side of the stipes, parallel to the 

 longitudinal ridges of the latter. Usually two roots are 

 formed on each stipes. Every longitudinal and transverse 

 section of the root-cell of the first degree appears triangular. 

 Its form is that of a low three-sided pyramid. It divides 

 by means of a concave septum turned towards its slightly 

 convex basal surface, and by this means lenticular cells are 

 formed, each of which becomes the mother-cell of two of 

 the cap-shaped cellular layers of the root-cap. The len- 

 ticular cell divides by longitudinal septa into four cells 

 standing cross-wise (PI. XXVII, fig. 10), after which trans- 

 verse septa are formed. In the middle of the circular 

 cellular layer, the further division by longitudinal septa 

 occurs more rapidly and more frequently than at the edges, 

 by which means the cellular surface assumes its cap-like 

 shape. Between the older of these cellular layers, whose 

 outer walls become very much thickened, intercellular 

 spaces filled with air make their appearance ; this is the 

 first commencement of the falling off of the cellular layers 

 of the root-cap, which decay by degrees from the outside. 

 Each division which is produced by means of a concave 

 septum turned towards the basal surface of the cell of the 

 first degree, is followed by three divisions of the latter, by 

 means of septa successively parallel to each of its three 

 lateral surfaces. The three cells of the second degree thus 

 formed, and which stand in a triangle, divide by means of 

 longitudinal and transverse septa, the division being more 

 active in that portion of them which is more distant from 

 the longitudinal axis of the root. The short-celled tissue 

 here formed becomes the cortical layer, whose early growth 

 is afterwards overtaken by the rapid longitudinal expansion 

 of the axile cellular tissue of the root during the transfor- 

 mation of the latter into the central vascular bundle* 



It is only in very rare instances that the terminal bud of 

 the stem of Aspidium jilix-mas divides by true forking of the 



* In consequence of my having examined seetions which were not truly 

 axile, I was led to assume that the lenticular cells of the interior of the root of 

 Equisetum variegatum (' Vergl. TJnters.,' pi. xviii, fig. 3), as well as the primary 

 cells of one of the layers of the root-cap, were root-cells of the first degree. 



