Igor] GERMINATION OF SPORES 39 
A few phanerogams which have become adapted to a peculiar 
environment may require a stimulus of this environment. Koch’ 
and Heinricher? have shown that seeds of Orobanchaceze ger- 
minate only with the presence of a host plant. Heinricher found 
that the seed usually germinates in spring or autumn, in periods 
of greatest humidity. He states that the germination of the 
seed is indirectly a partial indicator of the health of the host — 
a substance excreted by the latter being evidently the source of 
the stimulus. What may be the nature of this attractive sub- 
stance has not been determined. On the other hand, seeds of 
Rhinanthus seem to germinate without such stimulus. 
According to Wiesner 3 the seeds of Viscum album are known 
to germinate only in light, and although apparently mature in 
autumn, they are not to be forced to germination until the fol- 
lowing spring. The same was found true of Loranthus Europaeus ; 
and, although light is required for germination, the most favor- 
able conditions of the tropical climate of Buitenzorg could not 
induce this activity without the intervention of the resting period. 
Wiesner then surmised that the factors concerned are the grad- 
ual availability of the reserve food, a phylogenetic light influ- 
ence, and the effect of the viscous substance of the integuments. 
If there are other phanerogams growing in peculiar situations 
for which a particular stimulus is necessary for germination, the 
matter seems to await study. We cannot appropriately include 
in this place seeds of some Rosaceae, for example, which germi- 
nate better after passing through the digestive tract of birds, or 
after artificial treatment with acids. 
The germination of pollen has been very much studied, and 
it is Surprising that this has yielded so little of special inter- 
est relative to particular or peculiar stimuli. It is of special 
es: Kocn, L.: Die Entwickelungsgeschichte der Orobanchen 119. 1887. Heidel- 
*HEINRICHER, E.: Die Keimung von Lathrea. Ber. d. deut. bot. Gesells. 
12: 117-132. 1894. : 
* Wiesner, J.: Vergleichende physiologische Studien iiber die Keimung europii- 
on und tropischer Arten von Viscum und Loranthus. Sitzb. d. kaisl. Akad. d. 
Ssenschaften zu Wien 103 : 423-437. 1894. 
