[ 466 ] 



LXII. — ON APOSPOKY IN THE THALLOPHYTA. By W. E. 

 M'NAB, M.D., F.L.S. ; Professor of Botany, Eoyal CoUege 

 of Science ; Scientific Superintendent of the Eoyal Botanic 

 Garden, Glasnevin ; and Consultmg Botanist to the Eoyal 

 Dublm Society. 



[Eead, May 18, 1885.] 



Mr. Druery's remarkable discovery of Apospory {Journal of Linn. 

 Soc, vol. xxi., pp. 354, 358, and 360) may help to explain certain 

 peculiarities observed in the Peronosporese and also in Yaucheria. 

 As apogamy is not limited to the higher plants, it is therefore most 

 natural to expect the occurrence of apospory in the Thallophyta. 

 As apospory seems to be a very peculiar change occurring only 

 under certain special conditions, it is not to be expected that the 

 process will be common in the Thallophyta ; and the two sets of 

 examples here brought forward as apospory are both met with in 

 highly specialized non-cellular plants, the one being a green Alga, 

 the other instances being from a remarkable group of parasitic 

 Fungi. 



In Cystojius candidus there is produced below the epidermis of 

 its host a moniliform series of cells, and the cells of this series may 

 become separate when mature. These cells are almost always 

 described as conidia. Yan Tieghem {Traite de Botnnique, p. 1021) 

 simply calls them spores, while Yines in the fourth edition of 

 Prantl's Botany calls them sporangia. That they cannot be coni- 

 dia is abundantly evident from the fact that the contents escape 

 as ciliated zoospores ; while conidia seem always to germinate di- 

 rectly, by sending out one or more tubular prolongations. By 

 comparing the closely allied genus Achlya with Cystopus, the 

 necessary proof seems to be obtained of the identity of the zoo- 

 sporangia of Achlya with the so-called conidia or spores of Cysto- 

 pus. The single terminal bodies of Peronospora, and the some- 

 what similar bodies in Phytophthora maj^ also be regarded as true 

 sporangia, although there is a special peculiarity in Cystopus ; 

 namely, that the sporangia are superposed to one another in a 



I 



