222 Marshall Ward. — Structure of Puccini a Graminis. 
before the lower ones of the same series. The successive 
development of spores continues for some time; the young 
crowded spores assume polygonal shapes, but they round 
off as they ripen and their walls thicken. I have repeatedly 
examined these aecidia in the youngest stages discernible, 
and can find no trace of sexual organs ; the search for 
such organs has been equally unsuccessful in aecidia of 
other species — e. g. those on Ranunculus and on Tussilago. 
The basidia clearly arise from a tufted felt of mycelium, 
continuous with that in the tissues of the leaf, but no defi- 
nite organs of the nature of sexual organs were discovered. 
The aecidiospores will germinate readily in water on the 
leaves of the wheat, and their germ-tubes enter the stomata, 
and develop a mycelium which gives rise to the uredospores 
and eventually to the teleutospores of Puccinia Graminis . 
(Zeiss E.) 
Fig. it. A portion of a very thin section through a spermo- 
gonium (Zeiss E). To the right below a filament and its 
spermatium more highly magnified (Zeiss J). 
