478 THE FUNGI WHICH CAUSE PLANT DISEASE 



Dictyosporx: spores septate, both crosswise and lengthwise, i. e., 

 muriform. 

 Hyalodictyae: spores hyaline, muriform. 

 Phsodictyae: spores dark, muriform. 

 Scolecosporse: spores needle-shaped to filiform, continuous or septate. 

 Helicosporse: spores spirally twisted, hyaline or dark, continuous or 



septate. 

 Staurosporse: spores stellate or radiate, hyaline or dark, continuous 

 or septate. 



The mode of bearing spores and the color of the fungus both of 

 which it is seen are made the basis of classification have been shown 

 by Stevens and Hall ^ and others * to'depend largely on environ- 

 ment, while the septation of the spores, also a fundamental char- 

 acter in present classification, depends often on the age of the 

 spores or on other factors. Many spores are unicellular until 

 germination begins but then become tjrpically 2-celled; e. g., 

 Gloeosporium. Such conditions have led to much inaccuracy in 

 description and doubtless to undue multiplication of form- 

 species. 



It has been quite customary, probably to some extent excusably 

 so, to describe as new a form-species when no form-species pre- 

 viously described for the same host or its near botanical kin could 

 be regarded as identical with it. Thus a Septoria found on Vitis 

 would ordinarily be regarded as new imless some of the Septorias 

 already described on some of the Vitaceae seemed to be the same, 

 even though indistinguishable from dozens of Septorias on other 

 families of plants. This course has led to enormous multiplica- 

 tion of so-called species in these form-genera giving rise to such 

 form-genera as Septoria, Cercospora, and Phyllosticta with species 

 numbering more than 900, 500, 800, respectively. 



The condition is much as is depicted by Cobb:* "Is a fungus 

 species newly found on a peach? Call it new and name it pruni. 

 Same genus on the grape — ^name it ampelinum. On the apple? 

 New, call it mali. On banana? Christen it musse. What next? 

 Sparrow in a pear tree, Passer pjri?" 



Many of the form-genera are purely artificial— not at all well 

 founded, e. g., Phoma is separated from Phyllosticta only by the 

 supposed inability of the latter to grow on structures other than 



