Philip: The Uredinee. 385 
I found in this district an abundance of infected Polygonum 
amphibium, but sought in vain for any cluster-cups on the 
Geranium. Mr. W. B. Grove of Birmingham informs me that 
this Aicidium has never been recorded anywhere in England. 
It would seem then that this particular species is able in this 
country to dispense with the ecidial portion of its life. 
Among the puzzles which are requiring solution is the 
question Dr. Plowright asks: ‘ Why are some species heterce- 
cious and others not ? ’’ and then proceeds to suggest one reason 
apparently without much consideration, that those which are 
hetercecious occur upon host plants, with cuticles hard and 
difficult to pierce, as Carices, etc. If this means anything at 
all, it means that the germ tube being unable to penetrate the 
hard cuticle is obliged to seek another plant whose epidermis 
does not present the same difficulties. There are two objections 
to this suggestion—(r1) if the germ tube of the promycelial spore 
arising from the teleutospore cannot penetrate the hard cuticle, 
how did the previous germ tube of the ecidiospore find its way 
in? (2) it seems probable that no cuticle can be penetrated 
by the germ tubes of the fungus ; since they really find their 
way in by way of the stomata, and if the burglar can get in at 
the window the comparative weakness or strength of the wall 
is immaterial. One apparently obvious cause of hetercecism 
is that a fungus growing on a deciduous plant, whose leaves die 
down in autumn must, if it is to survive the winter, find a 
fresh means of subsistence during that period. This explana- 
tion fits absolutely such a case as Puccinia phragmitis; the 
eecidium on the dock would if it continued as teleutospores on 
the same plant be liable to perish along with the spring leaves, 
but on the stems of the reed, even when they are dry, finds 
means of existence until the arrival of spring enables it to return 
to the dock; but to assert that this is a full and adequate 
explanation of hetercecism in the Uredinez would be exceedingly 
rash. For instance, how does it help us in the double life history 
of Puccinia poarum which goes through the three series—ecidio- 
spores on coltsfoot, and uredo- and teleutospores on poa grasses, 
twice in the year? Only one of these series of metamorphoses 
can be accounted for by tiding over the winter; and again, 
as regards the Uredine known to Plowright as Puccinia rubi- 
govera. This is a yellow rust on the stems and leaves of wheat, 
rye, and some grasses. Plowright found that this rust produces 
an ecidium on Lycopsis arvensis, while Klebahn tells us that 
the yellow rust hitherto known as P. rubigo vera really consists 
of several distinct species on various graminaceous hosis. Of 
these he selects the one having its ecidium stage on Lycopsis 
arvensis and teleutospores on the rye, for the name of Puccinia 
dispersa. This species appears as an ecidium in September, 
the rye being then cut, and the rosettes of the Lycopsis appear- 
1git Nov. 1. 
255 
