304 
Mycologia 
genus Uredinopsis, however, the aecia are indehiscent. It seems 
quite probable, moreover, that in genera which typically open to 
the exterior the occurrence of internal aecia is not at all uncommon 
and that this phenomenon has been previously observed by those 
who have studied rusts. Their occurrence in Lycopus virginicus, 
however, has not previously been recorded. Neither are there 
published accounts of their presence in other hosts so far as can 
be learned from the available literature relative to rusts. Uromyces 
Caladii (Schw.) Farl. is known^ to form internal cluster cups in 
Peltandra virginica (L.) Kunth., and Reddick has observed them 
too in the fruits of the barberry. Not only it is probable that aecia 
quite commonly open within affected host tissues but also other 
stages of rusts as well. Puccinia graminis Pers. on rye bears 
uredinia, some of which liberate the uredospores into the interior 
of the hollow sterns.^ 
A satisfactory explanation of the causes for the production of 
internal aecia cannot be given at this time further than to state 
that they must be the same as those which bring about the pro- 
duction of external aecia. In case the cluster cups of P. angustata 
originate near the center of the stem they must of necessity open 
within the stem. Those more deeply seated might push inward 
and open toward the center of the stem because there was less 
mechanical resistance than toward the outside. Rusts, whose 
spore forms are typically internal, depend upon the weathering 
away of overlying tissues for the liberation of the spores. The 
internal aecia of P. angustata are to be regarded, however, as the 
abnormal rather than as the typical condition and the surrounding 
host tissue cannot then serve this protective function. 
Alabama Polytechnic Institute, 
Auburn, Ala. 
2 This observation was made by Prof. G. F. Atkinson, Cornell University, 
Dr. C. W. Edgerton, La. Exp. Station, and Dr. Donald Reddick, Cornell Uni- 
versity, from material collected at Ithaca, N. Y. Thanks are due the above 
gentlemen for this information so kindly given in letters. 
3 A preparation showing internal uredinia was loaned through the courtesy 
of Dr. Donald Reddick, Cornell University. 
