a 
-a a. 
ON THE STEM OF DAMMARA ROBUSTA. 449 
of the ground-tissue: this may be observed if the ends of roots 
be cut off, in which case an offset grows from the side above 
the divided healing surface. But in addition to this there is 
produced, after a while, a regular zone of sclerenchyma as an 
adjunct in the repair. 
The sclerenchyma is of more or less flattened muriform cells, 
Which sometimes are many layers deep, formed from the phellogen 
beneath the earlier cork-formation ; and as cork is again produced 
from the phellogen beneath the sclerenchyma, the latter comes at 
length to lie in the midst of the corky covering of the cicatrized 
surface. Such sclerenchyma I have observed also to be formed 
from the reparative phellogen in many Cactacee, Cereus, Opuntia, 
&e.; and it may be found also in the cork that repairs the old 
leaf-scars in Aucuba. 
The fact is of a little present interest, since Carruthers de- 
scribes the rhomboidal leaf-scars in the fossil form Lepidodendron 
selaginoides as showing that healing had occurred by the pro- 
duction of a “layer of small thickened cells ;” * and in the older 
scars of Dammara, as before described, flattened sclerenchyma is 
found in the substance of the cork. . 
[Nore.—The author has perhaps scarcely laid sufficient stress 
on the distinctive characters of the structures which in many 
Species of Selaginella give origin to the roots, and which Nägeli 
named Rhizophores. These “ arise very near the punctum vege- 
‘ationis, probably at the same time as the branches; unlike the 
roots, they are exogenous structures which, when young, possess 
a distinct apical cell.” From these rhizophores * the first rudi- 
ments of the true roots originate, which, however, do not break 
through until the rhizophore has attained such a length by inter- 
calary growth, that its smaller end penetrates into the ground. 
The rhizophores, as Pfeffer has shown (in S. Martensii, inequali- 
Jolia, and levigata), are often transformed into true leafy shoots, 
Which at first show some deviations from the normal structure in 
their leaves, but afterwards continue to grow as normal shoots, 
and even produce sporangiferous spikes.” (Sachs, ‘Textbook,’ 
2nd Engl. ed. pp. 477, 478.) . 
The author remarks that though the number of cases in which 
branches suffer disarticulation in the manner of leaves is now 
Somewhat numerous, it is difficult to find parallels in the case of 
* Monthly Microscopical Journal, Oct. 1, 1869, p. 181. 
