K.— BOTANY. 193 



which bear them. The cases of highly specialised entomophily where the 

 insect passes from flower to flower on the same inflorescence, and the 

 formation of dwarf males from the egg-bearing plant of Oedogonium are 

 examples of the same problem. 



Among the Discomycetes Dodge^^ in 1920 reported in Ascoholus 

 magnijicus the development of antheridia and oogonia along the line of 

 junction of two mycelia. Though the oogonium is globose, the trichogyne 

 here is long and septate, and coils round the antheridium ; but details of 

 fertilisation are not available, nor has it been finally ascertained that the 

 sexual organs originate only on hyphse of different strains. If the latter 

 should prove to be the case, simple dioecism is indicated, and this is borne 

 out by the fact that, as in the Mucorales, the sexual organs do not appear 

 till opposing mycelia have made contact. The same criterion applies in 

 the case of Ascoholus carbonarius,^^ where the trichogyne is even longer 

 and more richly septate, and the antheridium is described as conidial ; 

 apart from the fact that ascocarps arise where two strains meet, nothing is 

 known of the dioecism or heterothallism of this form. Ascoholus furfuraceus 

 and several other species produce fruits in single spore culture. 



As early as 1914 Egerton*" described in Glomerella cingulata, one 

 of the Sphaeriales, a phenomenon which may possibly fall into line with 

 more recent observations. In this fungus there are two strains which 

 differ in appearance ; that designated as (+) grows rapidly, develops 

 white or light grey aerial hyphae and produces a few perithecia which reach 

 normal maturity. On the ( — ) strain aerial filaments are scanty, while 

 perithecia are numerous, but asci do not ripen in culture except on acidified 

 oat agar, and even then are irregular in form. Where the two strains 

 meet fertile perithecia are abundant. Moreover, the asci in perithecia 

 on a (+) or a ( — ) mycelium produce only corresponding spores, whereas 

 those in perithecia along the line of junction have been shown to contain 

 spores of both kinds. Here it seems evident, not only that some stimulus 

 is conveyed by the association of two mycelia, but, since the (+) and ( — ) 

 characters are inherited through the ascus, that a mingling and ultimately 

 a fusion of (+) and ( — ) nuclei can take place. The species is remarkable 

 for the morphological difference of its (+) and ( — ) strains. 



A more orthodox case of heterothallism — using the term in its simplest 

 sense to indicate the presence of two or more kinds of mycelia — was 

 described by Derx*^ in 1926 for Penicillium luteum. In this fungus twelve 

 mycelia were grown from single ascospores ; perithecia were developed 

 only where two appropriate mycelia met, and these mycelia were further 

 differentiated by their feebleness or vigour. An energetic mycelium, 

 growing alone, gave rise to ascocarps, though without asci, liquefied 

 gelatine, and stained the substratum bright orange ; a feeble mycelium 

 showed none of these activities. When two vigorous mycelia, one (+) 

 and one (— ), were brought into contact, large numbers of perithecia 

 appeared ; when two feeble mycelia met the perithecia were but few, 

 while one vigorous and one feeble strain gave an intermediate supply. 

 Evidently, apart from the (+) and (— ) character, some nutritive factor 

 is here at work. 



In Giberella*'^ also, the ascigerous stage of Fusarium moniliforme, and 

 in Ophiobolus cariceti,^^ a cause of tahe all or whitehead disease on wheat, 



1928 O 



