On the Besting -Spores of certain Fungi. 33 



occurrence of antheridia in the same genera, closely resembling 

 those which were lately described in the Intellectual Observer, 

 in the paper on "3?>gg Parasites;" and in most of the species, 

 though not in Peronospora infestans, the existence of little 

 suckers on the threads of the mycelium, which perform appa- 

 rently a material part in the imbibition of the juices of the 

 mother plant. * 



As Peronospora 'parasitica is a species which is to be met 

 with in every parish, if not on cabbages and turnip leaves, at 

 least on the common shepherd's purse, Capsella bursa pastoris, 

 where it frequently accompanies Oystopus candidus, which also 

 has its resting-spores, though very differently sculptured, I pur- 

 pose to reproduce more especially the illustrations of that 

 species. 



The mycelium of the Peronosporce runs freely amongst the tis- 

 sues of the leaves of the plants on which the species are parasitic, 

 especially the loose tissue of the under surface, either forcing its 

 way between the cells when they are in close contact, traversing 

 the intercellular cavities, or actually penetrating the cell-walls. 

 The mycelium throws up erect threads through the stomates of 

 the leaves, which, when they become free in the open air, are 

 more or less branched. They are sometimes repeatedly forked, 

 as in Peronospora viticola, Berk, and Curt., undoubtedly the 

 most highly developed species of the genus, sometimes merely 

 divided above for the purpose of bearing the acrospores or 

 conidia, as iu Peronospora curta, Berk, and Br., a species evi- 

 dently identical with P. pygmcea, De Bary. These threads are 

 in general even, but in Peronospora infestans they are swollen 

 at intervals. The ultimate divisions, which are straight or 

 uncinate, bear more or less elliptic or obovate spores (acros- 

 pores), with or without a terminal papilla. 



The acrospores propagate the parasite in different ways. 

 When placed upon a drop of Avater, or in a moist atmosphere, 

 they push out, a few hours after they are sown, from the apex, 

 or from some indifferent point, as in P. parasitica (Fig. 1), a 

 thread, much after the manner of the spores of many Sphserige; 

 and if it be the proper season for the growth of these parasites, 

 temperature and time seem to be of little or no consequence. 

 In the lettuce mould, P. gangliformis, Berk., the germination 

 invariably takes place at the terminal papilla. 



In some species, however, as the yellow rattle mould, 

 P. densa, and the anemone mould, P. curta, the protoplasm of 

 the spores first exhibits a number of globose cavities (vacuoles). 

 After a time, the whole mass oozes out from the apex (Figs. 

 5 — 7), where it assumes a globular form, and becomes invested 

 with a membrane. Soon after, it gives off a thick tube from 

 the point opposite to that at which it at first protruded. This 



VOL. VI. NO. T. D 



