497 
the A natomy of the Genus Selaginella. 
made observations that, instead of so-called rhizophores, which had been 
expected, they found small-leaved shoots in their place, thus apparently 
proving that rhizophores are of stem-like origin. No author, however, 
seems to have made a comparative anatomical and physiological study of 
such leafy shoots and rhizophores or aerial roots. 
In N. uncinata I have frequently observed true (although thin and small) 
twigs instead of roots or so-called rhizophores. These twigs bear small 
leaves in proportion to their size. The leaves are always at some distance 
from each other, such shoots having thus the appearance of the main stems. 
In one instance I noticed that such an organ was deprived of its leaves on 
a length of about 12 mm., which is rather considerable for such a thin shoot, 
the remaining part being further covered with leaves as described above. 
Such shoots branch in the usual way, producing at the proper places aerial 
roots. Without any further anatomical study one would be apt to suppose 
that the leafless part would have the construction of a rhizophore and the 
leafy part that of a stem. Such modifications, however, we only observe 
where normal twigs have been damaged or bruised in some way or other. 
Often it could be observed in S', uncinata (Fig. II, 1, a), and the writer 
noted it a few times in S. grandis (Fig. Ill, 5), S. inaequalifolia , S. Wilde - 
nowi, S. Kraussiana y S. serpens , and once in S. rubella , S. Bakeriana , and 
S. Douglasi. 
The anatomical construction of such shoots is exactly the same as that 
of the ordinary stem. The lacunae and trabeculae, which are never formed 
in the aerial roots, are present in the shoots as mentioned above, although 
smaller, in proportion to their size, than those in the larger stems. That part 
of the shoot which is leafless for a distance of 12 mm. also contains lacunae, 
and consequently some trabeculae, and is a long internode. Moreover, 
I observed in all cases that such a long internode is already positively 
heliotropic in its early youth, whereas the aerial root is negatively helio- 
tropic from its start. For a further comparison, the following drawings in 
Fig. II relating to 5 . uncinata are useful. 1 is an old shoot which has been 
bruised, and soon formed two little twigs, A, A 1 , which according to some 
investigators are rhizophores transformed into leafy branches ; A 1 has 
formed in the usual way one aerial root, B ; 2 is a section of the so-called 
metamorphosed rhizophore which has, as stated above, the same construction 
as an ordinary stem, although the trabeculae are somewhat shorter ; also the 
further part of the vascular bundle is the same as that of a stem ; 3 is a part 
of the main stem, drawn for comparison ; 4 is a cross-section of aerial root B ; 
5 is the epidermis and hypodermis of an ordinary aerial root, and 6 that 
of rhizophore B ; 7 is a cross-section of an ordinary young aerial root, 8 of a 
root developed in the soil, 9 and 10 the epidermis of a stem and of an 
aerial root ; and 1 1 shows the branching system of a root, entering the 
soil at *. 
