360 Blackman . — On the Fertilization , Alternation of 
comparable to the spore-mother-cell of the higher plants and to the tetra- 
spore-mother-cell in the Dictyotaceae. The gametophyte generation starts 
again in the teleutospore and is continued up to the ‘ fertile cell ’ (the cell 
bearing the mother-cells of the aecidiospores) in the aecidium ; while the 
sporophyte continues throughout the rest of the life-history, through the 
aecidiospores, the uredospores (if present), and up to the teleutospores again. 
Credit must be given to Maire (29 and 30) for having pointed out the 
resemblance between the nuclear history of the higher plants and that of 
the Uredineae. He believed, however, that the ‘ synkaryon’ was a special 
condition always brought about by the association of two daughter-nuclei. 
He considered the spermogonia and aecidia to be non-sexual in nature, and 
was ignorant of any process of fertilization such as has just been described 
for the aecidium of Phragmidium . 
The existence of actual histological differences between gametophyte 
and sporophyte is in full agreement with the usual rigid distinction which 
is to be observed between the two generations, both in heteroecious and 
autoecious forms. As is well known, the aecidiospore by infection gives rise 
only to a mycelium bearing uredospores or teleutospores, the uredospore 
gives rise to a mycelium bearing only uredospores again, or teleutospores. 
Again, the sporidium arising from the teleutospore gives rise by infection to 
a mycelium bearing only aecidiospores, if those are present in the life-history 
(i. e. in the eu- and -opsis forms) 1 . 
Apogamy. In the forms in which the aecidium is absent (< brachy -, 
lepto -, micro -, and hemi - forms) the sporidium produces a mycelium which 
gives rise directly to uredospores or teleutospores with paired nuclei. In 
such a case we have a transition from the sexual to the asexual generation 
without the intervention of the female reproductive organ, and thus it is 
clearly comparable to apogamy among the higher plants. Sapin-Trouffy 
has shown that the change from single to paired nuclei takes place in these 
cases in connexion with the formation of the uredospores, or of the teleuto- 
spores, if the former are absent. The exact cytological details have yet to be 
worked out. It may be that the binucleate condition is brought about by 
the interaction of two vegetative cells , as in the case of apogamy in Ferns 
investigated by Farmer, Moore, and Digby (14), where they found the 
nuclei of neighbouring prothallial cells fusing to form sporophytic tissue. 
A form like Puccmia Liliacearum , DC., seems, like some of the Ferns, to 
be only imperfectly apogamous, for though the aecidia have been described 
they do not seem to be usually present. 
Apospory . The peculiar cycle of development observed regularly in 
1 The very few observed cases of aberrations from the normal life-history, such as aecidiospores 
giving rise to a mycelium bearing aecidiospores again (A. P. Dietel, Zeit. fiir Pflanzenkrankheiten, iii, 
1893, p. 25; Flora, lxxxi, 1895, p. 394), require further investigation; such cases may possibly be 
due to a separation of the nuclei of the pair, as in Endophyllum. 
