PHYCOMYCETES 147 



of water may be employed, or I pint to 1250 gallons has been 

 sufficient to check the infection. Permanganate of potash is rather 

 a mild disinfectant as compared with formalin and it is necessary 

 to use i pound to 625 gallons. A stronger concentration dis- 

 colors slightly and the former strength is advised. Copper sulfate, 

 which is both a cheap and effective disinfectant, may be used, 

 of about the same strength as the permanganate of potash. Care 

 should be taken that this is not employed in a very much more 

 concentrated form, I pound to 250 gallons, for instance, resulting in 

 injury in the form of a burn. Unfortunately, however, this substance 

 attacks the arm of the tank and is therefore less desirable than 

 those previously referred to. A higher concentration of blue stone 

 is needed on account of the alkalinity of the water used. In dis- 

 tilled water, one part of blue stone to one million will be effective. 



IX. PERONOSPORALES 



DE BARY, A. Zur Kenntnis der Peronosporeen. Bot. Zeit. 39: 521-530, 537- 



544, 553-563, 569-578, 5 8 5-595> 601-609, 617-625. pL 5. 1881. 

 FARLOW, W. G. Enumeration of the Peronosporeae of the United States. 



Bot. Gaz. 8: 35-3 l 5, 3 2 7-337- 1883. 

 LUSTNER, G. Untersuchungen iiber die Peronospora-Epidemien der Jahre 



1905 und 1906. Ber. d. Konigl. Lehranstalt fur Wein-, Obst- und Gar- 



tenbau, Geisenheim a/Rh. (1906): 119-140. 

 ROSTOWZEW, S. J. Beitrage zur Kenntnis der Peronosporeen. Flora 92 : 



405-430. pi. 11-13. i93- 

 SCHROETER, J. Peronosporineae. Pflanzenfamilien (Engler u. Prantl) 1 (i* 



Abt): 108-119. figs. 92-102. 1893. 

 SWINGLE, W. T. Some Peronosporaceae in the Herbarium of the Division of 



Vegetable Pathology. Journ. Mycol. 7 : 109-130. 1892. 

 WILSON, G. W. Studies in North American Peronosporales. I. The Genus 



Albugo. Torrey Bot. Club Built. 34: 61-84. 1907. II. Phytophthoreae 



and Rhysotheceae. Ibid.: 387-416. 



The members of this order are entirely parasitic, many of 

 the species causing important diseases of cultivated plants. The 

 mycelium is well developed, siphonaceous, and, with exceptions 

 in one genus (Phytophthora), intercellular. The asexual spores, 

 which may in general be termed conidia, are produced upon 

 erect conidiophores, which are from the first, or which ultimately 

 become, aerial. The conidiophores may be simple or diversely 

 branched. The conidia germinate either by means of a germ 

 tube or by the production of motile spores, zoospores ; in the 



