432 Ganong . — The Comparative Morphology of 
tion of the different species, and on account of the condition 
of the seed, time of year, temperature, &c. In most forms, 
after the completion of germination, there is a pause, and 
some time elapses before the epicotyl appears : in many 
kinds which it is easy to germinate, it is very difficult to 
ensure development into the seedling-stage, which shows that 
the materials laid up in the seed make them to some extent 
independent of external conditions, but that when they must 
begin to rely upon the surroundings for further progress, 
they do not find these favourable. No doubt in the deserts, 
germination is more rapid than in our greenhouses, and one 
may suppose that the seedlings attain a considerable size 
before their first dry season arrives. 
To show the rate of germination, the following facts are 
selected. On March 20, 1895, series of seeds were planted in 
a greenhouse under given favourable conditions; they appeared 
above ground as follows : — Opmitia basilaris var. ramosa , in 
five days ; O. serpentina , nine days ; Echinocactus viridescens , 
fifteen days ; O. echinocarpa , nineteen days ; Mamillaria radiosa 
var. neo-mexicana , twenty days ; O. tetracantha , twenty-three 
days; Echinocereus phoeniceus , twenty-seven days ; E. pectinatus 
rigidissimus , twenty-nine days ; M. Grahami , twenty-nine 
days ; O . phaeacantha , fifty-two days. Some seeds of the 
above species did not germinate for a year ( O . echinocarpa 
and E. phoeniceus ), which is a phenomenon well known in 
other cases, and perhaps has an ecological meaning. None, 
however, came up in pots kept for a third year. I have made 
no observations upon the length of time Cactus-seeds retain 
their vitality. Pfeiffer 1 , however, states that seeds of three 
species sown nine years after ripening came up in fourteen to 
eighteen days. 
The seedling-growth is most rapid in Opuntia. In O. echino- 
carpa planted March 20, the epicotyl with leaves was 7 cm. 
long on June 13, and in May of the next year some were 
15 cm. long and 3.3 cm. broad. The growth of O. serpentina 
planted at the same time was nearly as rapid. 
1 Neuere Erfahrungen, p. 122. 
