1905] CHRISTMAN—SEXUAL REPRODUCTION IN RUSTS 273 
RicHARDs’? observations of acarpogonial branch in the young aecid- 
ium of U. Caladii and other forms favor this view. It is quite 
possible that the gametes in U. Caladii are borne on branches arising 
from such a carpogonium. The final settlement of these questions 
of affinity must await the study of further forms of the rusts and 
related fungi. It is especially important, as suggested above, that 
the nuclear phenomena in species of rust with an abridged life 
cycle be determined. There can be no doubt that the proof 
given above of the existence of a sexual fusion of gametes in the 
aecidium finally disposes of the conception of DANGEARD’ and 
APPIN-TRourry* that the teleutospore is an egg, and the nuclear 
fusion which occurs in it the equivalent of the sexual fusions else- 
where among the algae and fungi. On the other hand, these discov- 
eries also confirm and give‘new significance to the conceptions, so 
clearly set forth by ArTHuR,> that the aecidium represents the stage 
of sexual rejuvenescence. There can be no question that BLACKMAN 
is in general correct in the contention that the nuclear phenomena in 
the teleutospore are concerned with chromosome reduction and mark 
the close of a sporophyte generation which began with the cell fusion 
in the aecidium. Here again; we need further facts as to the 
Tusts with reduced life cycle before the doctrine of an alternation of 
generations, such as BLACKMAN maintains, can be regarded as finally 
established. 
Matre’s® conception that*the nuclear fusion in the teleutospore 
is a mixie, was developed on the basis of the belief that no real cell 
fusion occurs in the life cycle of the rusts. It is at least a fair pre- 
sumption that while no nuclear fusion occurs in the aecidium, the 
fusion of gamete cells described above presents all the essential 
* Ricuarps, H. M., On some points in the development of the aecidia. Proc. 
Amer. Acad. a descien. $2 ho 1806. 
poy PA Tie siesbet sexuelle des champignons. Le Botaniste, 
7:89~1 30. 
7 “Sarr Taovre M., Recherches histologiques sur la famille des Urédinées. 
Otaniste 5: 59-244. figs. 69. 1896-97. 
a a . C., The aecidium as a device to restore vigor to the fungus. 
on Agric. Sci., 23d annual meeting. 
6 ‘ sei 
. Marre, R., Recherches cytologiques et taxonomiques sur les Basidiomycetes. 
go2. 
Proc. 
