28 TETRASPORE-MOTHER-CELL 
The teleutospore-cell is a spore-mother-cell, exactly com- 
parable with a tetraspore-mother-cell. The “ basidium” is merely 
the same cell, removed outside the old outer cell-wall for the 
convenience of the ensuing processes; in Coleosporium this 
removal does not take place, but the “basidium” is formed 
internally, the mucilaginous ‘nature of the cell-walls of the 
teleutospores of that genus allowing the sterigmata to protrude 
through them (see Fig. 241), which could not be done through 
the hard cutinised cell-walls of the teleutospores of Puccinia 
Caricis. 
The first division of the nucleus of the teleutospore is 
heterotypic, and really initiates the gametophyte; but, since 
this is not a sufficiently definite point in the cycle, it is usual 
to consider the gametophyte to begin after the next division, 
Le. by the formation of the four basidium cells, which constitute 
a tetrad. These four cells are the true tetraspores. In water, 
deprived of air, they can each send out a germ-tube and, it is 
presumable, could cause infection. The formation of basidio- 
spores on sterigmata is a secondary process, viz. the production 
of conidia suitable for wind-dispersion: this is shown by the 
fact that, if the basidiospores are not on the proper host plant, 
they can themselves germinate with the production of fresh 
conidia of an exactly similar character. 
The mycelium (thallus) of the gametophyte, issuing from 
the basidiospores, bears male and female organs, the spermo- 
gones and excidia. The spermatia disintegrate without any 
result: the “fertile” cells of the zcidium (usually, perhaps 
nearly always, after cutting off a sterile cell, as is the habit of 
female gametes) are stimulated to further growth by con- 
jugation with one another, the delay in the fusion of the nuclei 
being of little or no importance from this point of view. This 
so-formed fusion-cell is a zygote and is the beginning of the 
sporophyte. The zcidiospores and uredospores which are borne 
by this are conidial forms, devoted to increased multiplication, 
and may continue indefinitely till the time arises for beginning 
the cycle again. This is indicated by the dotted lines on the 
left of the diagram. 
It is known that a fusion of two nuclei, comparable with that 
