CLASSIFICATION OF FUNGI 37 



is P. palmivorum, Butler, which is the cause of the 

 Godavari disease of India (page 206). 



Pythiacystis citrophtliora, E. E. Smith, is the cause 

 of a disease of the lemon and other citrus fruits. The 

 fungus is a very much branched, irregular mycelium, 

 which penetrates the peel of the fruit. The conidia 

 are somewhat subspherical with a very prominent point 

 at one end. They germinate and produce a number of 

 zoospores. 



Order 5. PERONOSPORALES. - - The species of this 

 order are parasitic, most of them living on the higher 

 plants and some of them being the causes of very 

 destructive diseases. They are more highly developed 

 than the preceding, since they cannot be considered 

 either aquatic or semi-aquatic, but have adapted them- 

 selves to aerial conditions. However, they still require 

 a moist atmosphere. The mycelia penetrate the plant, 

 branch, spread, and send small suckers (haustoria) into 

 the cells. This ravenous method of feeding results in 

 the early death of the diseased parts and sometimes of 

 the entire plant. In time mycelial threads grow out 

 through the stomata, branch profusely, and bear conidial 

 spores. The spores are readily carried by the wind, and 

 when they fall upon suitable host plants and under 

 proper conditions of temperature and moisture they 

 either grow directly into a mycelial thread, which 

 penetrates the plant, or they produce zoospores which 

 swim for a time in the moisture and then grow into 

 mycelia. In some species the formation of the oospore 

 or egg spore within the tissues of the host is well under- 

 stood, but in other species it is unknown and is probably 

 not formed. Where known it is very similar in char- 

 acter to the preceding. Some of these fungi also cause 

 the damping off of seedlings and attack many mature 

 and hardy plants. 



Under this order we will consider two families, 

 Albuginaceae and Peronosporaceae. The Albuginaceae 

 contains but one genus Albugo (or Cystopus), or the 

 so-called white rust (Fig. 23). The mycelium penetrates 



