84 FIRST FORMS OF VEGETATION. 
In the morning the fronds are green, but as the 
day advances they become pale, recovering gradu- 
ally their colour by the following day. Dr. 
Hooker has observed that in their pale condition 
the chlorophyll of the cells of the leaves is con- 
tracted into a little pellet. This phenomenon is 
of the same nature as that which has been already 
described in connexion with the chlorophyll move- 
ments in the cells of mosses and hepaticae under 
the stimulus of light. The colour of some Lyco- 
pods is of a bluish metallic tinge, and seems to de- 
pend upon the effect of the different arrangement 
of the chlorophyll in the cells of the leaves upon 
the light. 
The club-mosses bear in the axils of their 
leaves minute round or kidney-shaped cases of a 
bright yellow colour, which form the receptacles 
of their dust-like seed. Some species have little 
cone-like spikes at the tips of their branches, 
under the scales of which, as in the pine tribe, 
lurk the reproductive embryos. In the common 
club-moss these spikes are two-pronged, and of a 
whitish colour, while the seed is highly inflam- 
mable, and was formerly employed to produce 
artificial lightning on the stage, by being blown 
through a tube and ignited. It is equally re- 
markable for the way in which it repels moisture, 
and for this reason it is employed by druggists in 
