f)48 Scientific Proceedings, Roi/al Dublin Society. 



distant ab illis hyphis quee ilia antheridia giguuut partes inferiores intra 

 antberidia superiores autem iu summis antheridiis babentibus oosporis 

 spbsericis crasso subfusculo episporio prseditis 29^-30/^. Invenitur inter 

 tuberis cellulas Solani tuberosi quas enecat. Hse cellulse tubere secto ad serem 

 nudatsB colorem primo rubescentem postea prope nigresceutem pree se ferunt. 

 Hah. in Hiberuia besperia et boreali. 



V. GrROWTH OF THE FuNGUS ON VARIOUS MeDIA. 



In addition to growing on living Potatoes, Turnips, and to some extent 

 on Swedes and Mangels, tins fungus can be cultivated witli ease as a 

 sapropbyte ; indeed, its culture in tbis way bas proved more easy tban tbat of 

 any one of some balf-dozen or more species of tbe genus Pbytopbtbora 

 wbicb bave been cultivated simultaneously witb it for comparative purposes. 



Particularly in regard to tbe formation of sexual organs and conidia, 

 bowever, it appears to possess predilections for certain media; audit would 

 probably prove an excellent subject for an experimental study of tbe factors 

 wbicb govern tbe development of reproductive organs, both sexual and 

 asexual. Up to tbe present, bowever, no attempts bave been made to 

 cultivate tbe fungus on syntbetic media, or to study tbe elfect of tbe presence 

 or absence of definite substances on tbe production of conidia or sexual organs. 



On ordinary neutral or slightly alkaline hcef-cxtract-peptone-gelatine the 

 growth is better than tbat of P. Fagi, P. Gactorum, and P. Syviiigae, but it 

 cannot be described as luxuriant. It is almost entirely submerged, and no 

 reproductive organs are formed. 



On ordinary wort-gelatine (in which tbe acidity of tbe gelatine has not 

 been neutralized) a luxuriant growth is produced both submerged and aerial, 

 but no conidia or sexual organs are ever developed. An eight-day-old 

 Petri dish culture iu tbis medium is illustrated in fig. 9, Plate XLIII. Tbis 

 medium is a very useful one on which to keep purely vegetative stocks of the 

 fungus running, by transfers at suitable intervals. If tbe acidity of tbe 

 gelatine be neutralized, tbe fungus grows just as well as before, and also 

 produces sexual organs, but not conidia. 



Tbe growth on tvort-agar is similar to tbat on neutralized wort-gelatine, 

 sexual organs being produced, but not conidia. 



On sterilized 2}ofato stalks, as well as on sterilized extract made from them, 

 tbe fungus grows well, both when tbe medium is used in liquid form and when 

 stiffened with gelatine or agar ; and sexual organs are produced fairly 

 abundantly, but not conidia. The various forms of media containing the 

 juices of parts of the potato-plant have, bowever, one disadvantage, which is 

 that, owing to oxidation during preparation and sterilization, they usually 



