THE AMERICAN BOTANIST. 
17 
A Water-storing Plant.— The various species of 
cactus and many other fleshy or succulent plants store up 
more or less water in their tissues for use in dry seasons. 
A plant from the island of Guam, mentioned by W. E. 
Safford, seems to have solved the same problem in another 
way. This plant is an epiphyte and is known asDischidia 
puberula. Some of its fleshy leaves are modifiied into urn- 
like receptacles. These usually contain water and the 
adventitious roots from the stem often creep into them as 
if for nourishment or moisture. The water is probably 
not stored up for this purpose, but those who see adapta- 
tions in everything will doubtless make a verj- pretty 
story out of these facts. 
Do Species Die of Old Age.— Individual plants as 
w^ell as animals have their periods of youth, maturity and 
old age and w^hen the destructive forces at length tear 
down the organism faster than it can be built up, death 
ensues. Species being mere aggregations of individuals 
might seem, at first glance, to follow the same rule, but 
this is by no means proven although evidence that they 
do so has been offered. That the answer to this question 
has a very practical bearing upon every da^' life may be 
seen in the case of the potato. Recently British growers 
of the potato have raised the cry that many of the princi- 
pal varieties are dying out. If this is true, some other 
food plant will have to be selected to take its place. 
According to the new origin of species, evolution is con- 
stantly going on and new species originating. In this 
event there would come a time, theoreticalh', when any 
species may have to give way to a stronger one. We are 
all able to recall species that appear to be dying out, and 
this appears to be due to gradual changes in its surround- 
ings, but when man cultivates a species and protects it 
from its enemies there appears to be no reason why it 
should ever die out. 
