Fusaria of Potatoes 111 



to speak, be a good Fusarium provided all other ch racters of this genus 

 are well expressed by the organism. 



VARIABILITY IN THE FUSARIA 



Many of the morphological and physiological characters of the Fusaria 

 show marked variability, and at first seem to be of such a nature as to 

 discourage any attempt to treat these fungi on a morphological basis. 

 Thus Smith and Swingle (1904:27), in regard to their F. oxysporum, say: 



" This fungus showed a number of very striking variations. For this 



reason it is impossible to give a general description that will hold uni- 

 versally." And after quoting descriptions of eleven old species of Fusarium 

 from potatoes, the authors conclude as follows (1904:51) : "Judged by the 

 above descriptions, we have had a half dozen or more species of Fusarium 

 in our culture tubes, some of them /new species,' and yet all were the 

 product of a single spore. This does not mean that there have been in 

 our cultures any very wonderful transmutations of one thing into another, 

 but only that organisms respond to their environment, and that 'species 

 descriptions ' of the kind cited have not taken this fact into consideration, 

 and consequently are worthless for scientific purposes. This is not a new 

 idea, but it is a fact to which the attention of systematic mycologists 

 might be directed profitably at frequent intervals." 



Sometimes variability, for example in the type of conidia, is so great 

 that a student gives up hope of determining the actual type. Thus 

 Wilcox, Link, and Pool (1913:24) conclude their discussion on the form 

 of the conidia produced by their fungus 27 as follows: " All sorts of stages 

 are shown in the plate, so that each one can judge for himself, as it is 

 possible that one who has studied a great number of species of Fusarium 

 will be able to pick out the characteristic form which can be set aside for 

 this particular species." 



A great number of instances of variability in this group also could be 

 cited easily from the species presented in this paper. But it will suffice 

 to state here only those instances of variability which are, perhaps, most 

 important and more or less common: 



1. The type of the conidium varies in many Fusaria from micro- to 



27 F. tuberivorum Wilcox and Link, which according to Wollunweber (1913 c : 206) is identical with 

 F. trichothecioides Wr. 



