230 SUMMARY OF CURRENT RESEARCHES RELATING TO 



confirm), and on the absence of parapliyses, which, however, are 

 present, though difficult to make out, he considers that the genus 

 must be suppressed, and the species arranged under the old genus 

 Vibrisscea. 



Didymosphseria and Microthelia.*— The identity had been 

 suggested t by Dr. Kehm of the genus Didymosphceria of Pyrenomy- 

 cetes with Microthelia of lichens, and the suppression of the former 

 in favour of the latter and older name. G. v. Niessl is unable to 

 accept this view; but regards the former as a true genus of Pleo- 

 spore^e, a family made up of genera characterized as under : — 



1. Physalosjyora. Spores (ascospores) one-celled. 



2. Didymosphceria. Spores two-celled. 



3. Leptosphceria. Spores multicellular, septated transversely 

 only, arranged in one or more rows in the asci. 



4. Baphidophora. Spores multicellular, septated transversely, 

 arranged in threads or clusters in a straight or coiled bundle in the 

 asci. 



5. Pleospora. Spores multicellular, septated transversely and 

 longitudinally. 



Feronosporeae and Saprolegniese.ij: — Professor A. do Bary gives 

 a very detailed description of the sexual and non-sexual organs of 

 the various species included under the Peronosporese and Sapro- 

 legniese. 



Pythium de Baryanum is much the most widely distributed of 

 the Peronosporese, its thallus being very abundant in living tissues, 

 and in the intercellular spaces, not only in CruciferaB, but in plants 

 belonging to widely separated natural orders. It is a true parasite, 

 and extremely destructive to the host ; but it occurs also in great 

 abundance in the soil, in the form of mycelium, resting conidia, and 

 oospores. It is characteristic of the species that in the formation of 

 the zoosporangia and resting conidia, adjoining portions of the thallus 

 are nearly or entirely and permanently deprived of their protoplasm ; 

 the emptied portion usually becoming separated off by a septum. 

 The resting conidia resemble the zoosporangia in every respect 

 except the formation of the neck and of the zoospores. The average 

 diameter of the oogonia is 21-24.- yu,, and of the oospores 15-18 fji. As 

 soon as the fertilizing tube is formed which carries the contents of 

 the antheridium to the oogonium, the protoplasm in the former 

 separates into two layers, a denser granular central layer which 

 de Bary calls " gonoplasm," and a less dense, nearly homogeneous 

 parietal layer, the " periplasm." The former only appears to 

 participate in the actual process of impregnation. 



P. vexans de By. occurs in tubers of the potato which have been 

 partially destroyed by Phytophthora, and is closely related to, but 

 apparently not identical with, P. Equiseti, found by Sadebeck on the 



* Hedwigia, xx. (1881) pp. 161-6. 



t See this Journal, iii. (1880) p. 314. 



X A. de Bary, ' Beitr'age zur Morph. u. Phys. der Pilze,' Frankfurt a. M. 

 1881, pp. 1-71 (6 pis.); and Bot. Ztg. xxxix. (1881) pp. 521-30, 537-44, 553-63, 

 569-78, 585-95, 601-9, 617-25 (1 pi.). 



