368 HOFMEISTER, ON 



roots of such plants it is manifest that the uppermost roots 

 of the individual rows are the youngest, a fact which is 

 not so easily seen in Isoetes lacustris. In the three-furrowed 

 Tsoetes also the vascular bundles of the roots are excen- 

 trical ; they are pushed towards that side of the root which 

 is turned towards the cortical furrow in which the root 

 breaks forth. The yearly renewal of the bark by the de- 

 velopment of the mantle of cambium which also surrounds 

 the lower three-armed portion of the wood, causes the 

 removal of the older roots in a lateral direction away from 

 the indentation of the stem in which they first appeared, 

 and pushes them downwards and outwards. In the three- 

 furrowed species however this change of position is less 

 remarkable than m Isoetes lacustris. 



In the three-furrowed species the stem occasionally ex- 

 hibits a fourfold division ; this appears to happen most 

 frequently in Isoetes ienuissittia, I found it to occur in 

 two specimens out of seven. In stems of this sort the 

 lower portion of the woody mass is four-armed. 



The terminal bud of most of the three-furrowed Isoetes 

 is far more deeply buried than even in Isoetes lacustris 

 (PL LIII, fig. 21). This partly arises from the propor- 

 tionably greater number of the leaves, and the consequently 

 more rapid increase of the cortical tissue. One essential 

 cause of the phenomenon is, however, the circumstance that 

 the cambium-layer — which clothes the cylindrical portion 

 of the woody mass, and which becoming prominent at 

 three places, as in Isoetes lacustris, reaches to the outermost 

 ends of the upwardly- curved arms of the lower portion of 

 the wood — has far greater vigour, on account of the much 

 more considerable radius of the lower portion of the woody 

 mass. The activity of the numerous layers of eambial 

 cells, which are almost convex above, must necessarily in- 

 crease the mass of the bark more rapidly than is the case in 

 Isoetes lacustris. 



The leaves of the three-furrowed species, the multiplica- 

 tion of whose cells usually agrees with that of Isoetes 

 lacustris, exhibit a far greater variety in their morphology 

 and anatomy. The stipule-formation mentioned in a previ- 

 ous part of this chapter is an example of this. The most 



