25 1 
The Rhizophore of Selaginella. 
Kew specimens). Out of three organs which appeared, and which 
soon began forking, one was densely covered with root-hairs, no 
trace of which could be seen on the other two, hence this particular 
organ was in all probability a root and, to judge by the known facts 
in other cases, was probably borne on an exceedingly short rhizo¬ 
phore. But I did not investigate the matter more closely. The 
presence of rhizoids (root-hairs) on the “ protocorm ” of Lyco¬ 
podium does not, as Velenovsky maintains, necessarily support the 
idea that this organ is a root, for rhizoids occur on rhizomes of 
Psilotaceae and Hymenophyllaceae; it is also an interesting fact for 
the comparison between the “ protocorm ” and the rhizophore that 
Bruchmann observed and figured a rhizophore, produced from the 
hypocotyl of Selaginella Martensii, which bore rhizoids at its tip 
before the period at which the root-initials were laid down. 
When it first became evident to me that the rhizophore was of 
shoot-nature, I began to ask whether its position on the stem was 
in harmony with this conclusion. In 1892 Velenovsky discovered, 
for the first time in the vegetable kingdom, the phenomenon of 
tetrachotomy in certain species of Selaginella ; this consists in the 
presence immediately below each fork of the stem of two smaller 
shoots, one on the upper and the other on the lower side of the axis ; 
in fact, the stem here branches apically into four arms, all of equal 
value and two of which are in a plane at right angles to that of the 
other two and are shorter and later in appearance. Now these 
latter occupy the precise position of rhizophores and are, indeed, 
nothing else but rhizophores in a different guise. Hence we may 
conclude that in a typical Selaginella- stem the two rhizophores of 
each fork represent the two delayed and highly-modified arms of the 
tetrachotomous branching. Their very definite place of origin 
speaks strongly in favour of their shoot-nature. Indeed, there can 
be no doubt about it after all the facts are taken into consideration. 
As for the fossil organ Stigmaria belonging to the stems of the 
Lycopodiaceous genera Lepidodendron and Sigillaria, from what we 
know of its habit and structure, it is quite likely homologous both 
with the rhizophore of Selaginella and the “ protocorm ” of Lyco¬ 
podium. The organ under these three differentiated forms which 
can be given no distinctive name itself (although we recognise its 
probable shoot-nature), must be extremely ancient, even in its 
highly-modified form. But we should not wonder at finding highly- 
differentiated structures and organs in Palaeozoic times; the world 
was probably ancient enough even then. 
