426 



As regards the delimitation of the species it is plain that, 

 while there is a considerable amount of variety, the A-spores 

 tend to a great uniformity and are in themselves of little use. 

 But the spores as a whole, combined with the variations in 

 external appearance, and in the nature of the Diaporthe to which 

 the Phomopsis belongs, enable one to delimit the species with fair 

 success. . Yet it is also plain that, until the forms of Phomopsis 

 are all correlated with their ascophorous stage, it will be necessary 

 in many cases to rely on the host-plant for their identification. 



Further, there is sufficient evidence to make it highly probable 

 that the same species can attack any part of the same plant, not 

 only stems and branches, but twigs, petioles, leaves, fruits, and 

 even galls. 



Thus such a " species " as P. petiolorum (Desin.), supposed to 

 be confined to petioles, is an absurdity which must now be given 

 up. Its various forms must be assigned to one of the species of 

 Diaporthe that infest each particular host. A similar statement 

 may be ventured, among others, of P. glandicola on acorns, and 

 P. pterophila on ash-keys; as knowledge becomes more accurate, 

 we may expect these to be proved to be forms of some species on 

 oak and ash respectively. 



Some authors would take us further still in this simplifying 

 process. It is known to all mycologists that the genus Diaporthe 

 was divided by Nitschke and Saccardo into three subgenera : 

 (1) Chorostate, with clustered perithecia, (2) Euporthe, with 



scattered or gregarious perithecia immersed in the wood, and (3) 



Tetrastaga, with similar perithecia immersed in the bark; and it 

 was held by Saccardo that two species belonging to different 

 subgenera were different from one another, even though they 

 occurred on the same host. If, therefore, a Phomopsis belonged 

 to a Euporthe, it was considered to be different from a Phomopsis 

 that belonged to a Chorostate or a Tetrastaga on the same plant. 

 A good illustration is seen in P. oncostoma and P. Pseudacaciae, 

 on Robinia (see supra, p. 179). But if von Holm el had his way 

 (Annal. Mycoi. 1918) all this would be altered, and the three 

 subgenera yrould be considered to be growth-forms merely. Thus 

 the same species, on the same host, might have a Chorostate form, 

 a Euporthe form, and a Tetrastaga form. 



Nor is this the climax. He goes further and considers that, 

 not genera, but families, should be the biological basis of distinc- 

 tion. Thus all the species of Diaporthe (and consequently of 

 Phomopsis) on Sambucus, Viburnum, Lonicera, Symphoricarpus, 

 and Leycesteria, should be classed together under the title 

 D. spiculosa, Nits. This is lumping with a vengeance, and 

 probably few would be ready to go so far, without more evidence. 



It must be remembered that, with one exception, no cultures of 

 these genera have yet been made. Only let our friends, the 



petri-dish laboratory culturists, get to work and, judging b 

 what we see in that line to-day, the tendency will be very muc 

 the reverse of von HohneVs. The nine or ten species on Capri- 

 foliaceae, lumped by him under D. spiculosa, Nits., would more 

 likely be split up into innumerable biological races. Luckily 

 there is a limit to the capacity of one poor human brain : medio 

 tutissimus ibis. 



