NATURAL HISTORY SOCIETY OF GLASGOW. 211 



of Heme Bay; and in 1877, while preparing a slide to show the 

 vascular structure of the axis of Lepidodendron, he observed both 

 the mycelium and oogonia of a fungus, which Mr. Worthington 

 Smith subsequently described, naming it Peronosporites antiquarius. 

 A Mucor had been previously described from the Coal Measures, 

 and other fungi had occasionally been observed, though no definite 

 descriptions had been given. According to Mr. Smith, the 

 mycelium of this Peronosporites is clearly septate, and certain of 

 the oogonia show the contained zoospores "with a clearness" — to 

 use his own words — "not to be exceeded by any living specimen at 

 the present time." The oogonium is exactly the same in size and 

 character with that of our Peronospora infestans — the contained 

 zoospores are of the same form and dimensions, while the average 

 number of zoospores in each oogonium is the same. In tin's lowly 

 organism we have probably a simple primordial fungus. Perono- 

 spora is very closely related to the algae, the Saprolegnieae — which 

 unite the parasitic habit of moulds with the fructification of algae 

 — being the connecting link. Now Sachs and others place the 

 lower algae among the primeval plants from which fungi and 

 other cellular cryptogams have branched, and the extreme antiquity 

 of this closely-allied form — Peronosporites — lends much support to 

 their views. Were algae once to branch out in this way, we can 

 so far understand — if we accept the theory of evolution — how all 

 the variety and complexity that characterise the fungi arose 

 during the millions of years that have elapsed since, at the least, 

 the time when this Peronosporites lived. The lowly cellular 

 structure of these fungi would in itself probably indicate their 

 appearance at an early period in geological time, but this important 

 discovery has set the matter at rest. 



Nor is this Peronosporites by any means the oldest known 

 instance of vegetable parasitism, which has, besides, been observed 

 in fossils of both the Silurian and Devonian systems. Professor 

 P. M. Duncan describes an alga (Palaeachlya) found on Silurian 

 corals, w r hich agrees in shape and size with the form parasitic on 

 corals of the present time, known as Achhja, resembling Saprolecjnia 

 ferax in its habit; and he further considers Empusa, Saprolegnia , 

 and AcJdya to be the same organisms living under different 

 physical conditions. If such be the case, the wonderful persistence 

 of form in this lowly organism is deserving of attention. As 



further testimony to the intimate relationship between the alga- 

 VOL. iv. p 



