122 
j. C. Th. Uphof . 
Length in mm. of longitudinal sections of full-grown stems of 
xerophytic Selaginellas. 
Wet 
Dry 
Name 
Condition 
Equal 
length 
of both 
tissues 
Length of 
thick- 
walled 
tissues 
Length of 
thin- 
walled 
tissues 
5. pilifera 
dead, from Mexico 
•900 
•885 
•835 
S. pilifera ... 
living, from green¬ 
house 
1-200 
1-190 
•1140 
S. lepidophylla 
dead, from Mexico 
1-000 
•985 
•935 
S. lepidophylla 
living, from desert 
region 
•900 
•880 
•820 
S. cuspidata 
dead, from Mexico 
•900 
•880 
•825 
S. cuspidata 
living, from green¬ 
house 
1-000 
•975 
•950 
S. longispicata 
dead, from Mexico 
1-000 
•975 
•930 
S. Pringlei 
dead, from Mexico 
•900 
•885 
•840 
The movements of the tissues are entirely mechanical, as their 
cells when old do not contain living protoplasm even in living 
plants: moreover similar results are obtained in dead plants as is 
shown in the table. They depend upon the hygroscopic capacities 
of the tissues, being entirely physical instead of biophysical. After 
drying above a flame, the tissue soon absorbs moisture from the 
surrounding atmosphere in a damp climate. 
In 5. pilifera there is a well developed lacuna with well formed 
one or two-celled trabeculae round the bundle ; the trabeculae are 
thinner in individuals grown in a moist and shady environment. 
The proto- and metaxylem is well developed, although in 
proportion to the water supply of the stem. 
Plants which were grown in a Wardian case in a moist and 
shaded greenhouse at Kew show different structural characters. 
The leaves are further apart and do not lie so flat against the stem 
(Fig. I, 1, 2). The cell walls of the epidermis, hypodermis and 
cortex are considerably thinner; the cuticle however is only 
slightly thinner. There is not much difference in thickness of the 
walls between the tissues of the uppermost part and the lower 
surface ; consequently the stems do not fold up so much when dry. 
The tissues of the lower part of the stem are not impregnated with 
red brown pigment. Moreover the presence of suberin is less 
pronounced than in plants grown in a semi-arid environment. The 
intercellular spaces are larger and persist longer in plants grown 
in the greenhouse ; also protoplasm remains longer in the cells of 
