Generations , and General Cytology of the Uredineae. 335 
MYCELIUM AND SPERMOGONIA. 
Phragmidium violaceum. 
The mycelium which appears in the leaf soon after germination of 
the teleutospores is derived by infection from the sporidium, and soon 
bears the spermogonia ; it consists of numerous hyphae with single nuclei, 
which appear to be always enclosed in separate cells. Most of the hyphae 
are intercellular ; some penetrate the cells, but they appear to have no 
definite connexion with the nuclei of the host-cells, as in the haustoria 
described by Sapin-Trouffy for some forms. 
The spermogonia are found usually on the upper side only of the leaf. 
Like the aecidia they are of indefinite extent, and are to be found as 
simple layers of parallel spermatial hyphae developed beneath the cuticle. 
Each irregular layer or spermogonium can be distinguished into a number 
of slightly projecting ‘hummocks,’ above which the cuticle is perforated 
to form the ostiole. One of these ‘hummocks’ is shown in section in 
Fig. 46. The spermogonia have usually no paraphyses, but occasionally 
one or two spermatial hyphae may grow out as sterile threads and project 
through the aperture in the cuticle. 
The spermogonia are formed by hyphae which grow up between the 
epidermal cells, and form beneath the cuticle a mycelial bed, or plec- 
tenchyme, of uninucleate cells. From this there arises a compact mass 
of parallel spermatial hyphae. The spermatial hyphae of any given group 
all point their free ends towards the aperture in the cuticle in the centre 
of the hummock (Fig. 46). Each group of spermatial hyphae with its 
ostiole should probably be looked upon as a single spermogonium, several 
spermogonia being collected together to form a composite structure. The 
cuticle, which is of course pushed up by the growth of the hyphae, becomes 
very much thickened at these spots, and stains very deeply with the safranin 
of Flemming’s triple stain and with iron-haematoxylin (Fig. 46). 
Each spermatial hypha contains a single, usually elongated, nucleus 
with a chromatin network, one or two small nucleoli, and an indistinct 
membrane. The spermatia are budded off from the tips of the hyphae, 
a projection being first pushed out from the apex of the hypha, and when 
it has reached its full size the nucleus passes into it. The end of the 
hypha has a ring of special cell-wall, staining deeply with Congo-red, 
as in Gymnosporangium , which offers a much more favourable object for 
studying the development of the spermatia. 
The mature spermatia are minute uninucleate cells more or less oval 
in shape. Each contains a comparatively very large nucleus, which shows 
a dense chromatin network but no nucleolus; surrounding this is a thin 
