FROMME: SEXUAL FUSIONS IN FLAX RUST 119 
matiophores differ from those described by Blackman in that 
they are divided into a number of uninucleated cells, usually four, 
each of which puts out a fingerlike process from its upper end on 
the tip of which a single spermatium is produced. See Fic. 1 and 2. 
The spermatiophores of Gymnosporangium clavariaeforme and 
Phragmidium violaceum, as described by Blackman, are single 
elongated, uninucleated cells. The single nucleus divides suc- 
cessively to form the nuclei for a number of spermatia which are 
abstricted from the elongated fingerlike tip of the spermatiophore. 
Fic. 4 shows two spermatia fully formed while a nucleus still 
remains in the base of each cell. This seems to indicate that two 
or more generations of sporidia are produced from the same cell 
of the spermatiophore. 
AECIDIUM 
The aecidium arises from a uninucleated mycelium, which in 
the vegetative condition cannot be distinguished in any way from 
that which produces spermogonia. It is confined chiefly to the 
intercellular spaces of the host. The nuclei at this stage are 
rather small but exhibit a clearly defined chromatin network and a 
definite nucleole. After a period of vegetative development the 
filaments grow up between the cells of the mesophyll and reach 
the epidermis. Here they branch laterally to form a weft of 
hyphae. The branches next push up vertically and form a sort of 
Palisade of large cells which contain very large nuclei and more 
compact cytoplasm than the ordinary vegetative cells. See FIG. 5. 
Each cell now divides somewhat unequally, producing a smaller 
cell above, which again divides so that two smaller cells are 
formed above a single larger cell. See FIG. 5. The larger cells 
are the future gametes and at this stage form a rather even dense 
layer below the two sterile cells. The shape of the sterile cells 
1s determined by the pressure of the epidermis and that of the 
Surrounding cells. When they press directly against the epidermal 
cells they are flattened laterally and the upper cell conforms to the 
Outline of the overlying epidermal cell. At other points where 
Pressure is not so direct they may be somewhat elongated. 
, either case they soon become vacuolate and disappear usually 
. the time of sexual fusions. These are the “buffer” cells of 
‘istman, and we see that they are here in two layers instead of a 
Tn 
