496 Uphof. — Contributions towards a Knowledge of 
thickness) in S. rubella , Martensi , and S. decora ; while those of 
5. Wildenowi are as thick as 2-5 mm. and sometimes slightly more in 
diameter. 
The air-root of some species practically never branches before entering 
the soil, e.g. 5. uncinata , 5. rubella , S. formosa, and other species; on the 
other .hand, those of other species may branch when in the air, e. g. 
S. Wildenowi , rupestris , rupincola , and 6'. inaequalifolia. 
The length of the rootlets and entire root system in the soil depends 
greatly upon the presence of plant food, and also stands in close relation to 
the size of the air-roots, whose length may be considerable in some species, 
as is summarized in the following list : 
Length and diameter of air -roots of various Selaginellas. 
Name of Plant . 
S. molliceps 
S. patula 
S. decora 
S. viticulosa 
S. Wildenowi 
S. cuspidata 
S. pilifera 
. S. rupestris 
S. serpens 
S. Martensi 
S. rubella 
Length. 
Diam. 
Name of Plant. 
Length. 
Diam. 
mm. 
6-15 
mm. 
1 1 
3“2 
S. Bakeriana 
mm. 
6-12 
mm. 
1 1 
! 1 
3 2 
10-18 
1 3 
2~4 
S. uncinata 
35-40 
3°"45 
I- I 
S. inaequalifolia 
20-40 
1 3 
2 4 
3-8 
1 1 
4 3 
S. Kraussiana 
2 5~35 
1 3 
2 4 
90-260 
S. apus 
5-12 
1 1 
4 3 
5-8 
!-l| 
S. Douglasi 
20-28 
1 1 
u 
2 L 
5-8 
3 U 
4— 1 2 
S. grand is 
8-12 (20) 
4-8 
1 1 
3"* 2 
S. Galeotti 
80-120 
1 3 
2 4 
6-12 
1 1 
4 3 
S. formosa 
40-60 
1 3 
2 4 
30-60 
I" 1 
S. haematodes 
6-15 
1 1 
4 3 
30-65 
l-I 
S. sanguinolenta 
4-8 
1 1 
4 3 
Anatomically there is a marked difference between the air-roots and 
terrestrial roots on one hand, and the stem (especially of the heterophyllous 
species) on the other hand. Of the species whose anatomical construction 
is described below many sections of roots in various stages of development 
have been made, but no lacunae and no trabeculae, which are characteristic 
in stems of all heterophyllous species, have ever been encountered, and 
these sections show a very important differentiation as far as the anatomy 
is concerned. For this purpose longitudinal sections of air-roots with 
attachment of the stem were made by the writer from several species. 
Fig. IV, 1, shows such a section of 5. rubella , in which the difference 
between the two vascular bundles of both kinds of plant organs is clearly 
visible ; the bundle of the stem is above, that belonging to the air-root being 
on the left of the drawing. There are, however, according to some 
investigators, indications of the transformation of such aerial roots into leafy 
shoots, which would apparently prove that these organs are no real roots but 
shoots. Bruchmann (2) has observed in S. Kraussiana that when individuals 
which have been outside during the summer are in autumn put into a 
warmer environment these roots form at the apex stems with small leaves, 
as has been stated above ; also that other plants of other families may form 
leafy branches at their roofs. Also Pfeffer (9), and later Worsdell (17), have 
