42 Fraser. — Contributions to the Cytology of 
In 1905 Claussen (10) announced fertilization in Boudiera , and in the 
same year Harper (31) gave a very full account of the sexuality and general 
cytology of Phyllactinia . 
Besides these forms, in which the fusion of the sexual pronuclei was 
actually observed, several cases have been described among the lichens, 
the Laboulbeniaceae and the Ascomycetes generally, in which considerable 
evidence of such a process has been obtained. 
In 1906 the behaviour of the nuclei in a ‘ parthenogenetic ’ form, 
Humaria granulata, was observed (Blackman and Fraser (8)). An ascogonium 
but no antheridium is developed, and the female nuclei fuse in pairs before 
passing into the ascogenous hyphae. 
In 1907 a similar process was described by Welsford (4) for Ascobolus 
furfur aceus , and in the same year Lachnea ster corea (Fraser (21)) was 
added to the ‘parthenogenetic’ or homoiogamous forms. 1 In this case, 
however, reduction has progressed rather less far than in the others, since 
an antheridium is still present, though its nuclei degenerate in situ. 
In all these forms, whether normal or reduced, the ascogenous hyphae 
arise from the ascogonium only, and the nuclei which pass into them are 
formed by the fusion of postmeiotic nuclei in pairs. They constitute 
the sporophyte generation and develop parasitically at the expense of the 
gametophyte. 
The ascocarp of Humaria rutilans reaches maturity without the 
formation of sexual organs. In the hypothecium fusion of nuclei in pairs 
takes place. Ascogenous hyphae are then developed altogether similar 
to those which form the sporophyte in species with normal sexuality and 
moreover containing, as will be shown later, nuclei with the premeiotic 
number of chromosomes. 
Thus it appears that here also the ascogenous hyphae form the sporo- 
phyte and that the fusions in the hypothecium constitute a reduced sexual 
process comparable to that observed by Farmer and Digby (17) in the 
prothalli of Lastrea pseudomas vars. polydactyla. In Lastrea the cells are 
uninucleate and the nuclear fusion is preceded by migration ; this also 
is sometimes the case in Humaria , though, since the cells may be 
multinucleate, it perhaps does not always occur. 
Humaria rutilans is thus an example of the so-called apogamous 
development of the ascocarp, or pseudogamy. 
Probably a similar fusion of vegetative nuclei takes place in other 
Ascomycetes, such as Cordyceps and Claviceps , which have been described 
1 The various forms of reduced fertilization are grouped by Farmer and Digby (17) under the 
general term pseudcipogarriy. The diversity of such processes, among Fungi at any rate, having 
appeared to render desirable a further subdivision, the following terminology was recently (Fraser 
and Chambers (21 a)) suggested : — Fusion of two sexual nuclei of the same kind — hontoiogamy. 
Fusion of one sexual and one vegetative nucleus — hylogamy . Fusion of two vegetative nuclei — 
pseudogamy . 
