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Scientific Memoirs by
Chrysomyxa. But, although my attempts to reproduce either Æcidium on the two
species of Pinus have failed, I am not so confident that one or other may not
be caused by the Chrysomyxa, because their abundance runs parallel with the
abundance of the Rhododendron affection. Again, if I am correct in regard
- i n g t h e t w o Æ
i d i a
on the two species of Pinus as distinct, then, for the follow
- i n g r e a s o n s , I t h i n k t h a t o nP
. e x c e l s a
i s m o r e l i k e l y t o b e t h e o n e s o r e l a t e d .
The natural history of the P. longifolia Æcidium runs thus:—A few ripe
æcidia may be found on the needles as early as January and February, but
they become more and more abundant as time goes on, until in May it is ex
-ceedingly abundant. But at this time the needles which bear them, and which
were formed in the preceding spring, are rapidly falling off, and in June de
-foliation is complete. While this is going on new needles are being unfolded,
commencing in March, and by the time the old needles bearing the æcidia
have all fallen, the new ones are about one-half to three-quarters grown. These
new needles present no sign whatever of attack. The host, therefore, remains
free of the fungus until very early next spring, when the whole cycle of events
above described is repeated. Thus the æcidia begin to appear long before the
Chrysomyxa is ripe and continue to be formed, while the Chrysomyxa sporidia
are being shed, but only on the older needles. Hence if these sporidia give
r i s e t o t h e æ c i d i a , a t t a c k o f t h e n e w n e e d l e s m u s t t a k e p l a c e d u r i n g A p r i l a n d
May, although no outward Sign of it exists, and then a long peroid of latency of
the mycelium ensues until early next spring. This, however, appears to me to
be very improbable.1
The natural history of the Pinus excelsa Æcidium is much the same as
the above, but with these important differences. The æcidia do not appear
until April and May, when Chrysomyxa sporidia are beginning to be scattered, and
the needles are not shed annually. But here also only the needles unfolded in
the previous year are attacked, and never those formed at this time. In this case,
therefore, the season of the appearance of the æcidia makes it quite possible
that it is caused by the Chrysomyxa sporidia: both fungi appear and ripen simul
- t a n e o u s l y . I n t h i s c a s e w e d o n o t n e e d t o a s s u m e i n i t i a l a t t a c k , w i t h a s u b s e q u e n t
period of quiescence. However, as I have already noted, I have not been able
experimentally to produce attack in the needles with Chrysomyxa sporidia.
Conversely, I have often also tried to reproduce the Chrysomyxa on R hodo
- d e n d r o n b y l a y i n g t h e æ c i d i o s p o r e s f r o m b o t h s p e c i e s o f P i n u s o n t h e l e a v e s ,
but with no success.
Thus, though there is presumptive evidence to favour a view of connec
- t i o n b e t w e e n t h e Æ c i d i u m o nP
. e x c e l s a
a n d
C h r y s o m y x a H i m a l e n s e ,
experi
- m e n t a l e v i d e n c e , s o f a r , i s a g a i n s t i t . I f t h e c o n n e c t i o n d o e s n o t i n f a c t
exist, I am quite at a loss to guess what other host the sporidia attack. I have
1 As this paper was passing through the press I found that some few isolated fully ripe æcidia may
be found in autumn.