13 



variable peritheeia from pure cultures of the eoiiiilia, sometliiug vre 

 have uot yet learned to do with any certainty; or, linally, to discover 

 in nature the j^erfect fruit form and derive the other I'oinus from it. So 

 far as known to the writer, no Fusaria except those above mentioned 

 have been described from cotton, watermelon, or cowpea; but even if 

 they had, it would in the present stage of our knowledge be next to 

 impossible to establish identity beyond reasonable doubt, since many 

 species of Fusarium are believed to be purely saproi)hytic and are 

 known to grow on almost any dead substance, and one such form has 

 been discovered by the writer in Washington on a dead stem of cow- 

 pea in connection with the peritheeia of a Nectria. 



(3) Chhimydospores. — On the surface of the dead stems of the water- 

 melon and in old cultures of the melon fungus on horse dung, globose, 

 thin-walled, smooth, terminal or intercalary bodies ai)pear, and in mass 

 on the dung are brick red (I'l. Ill, 12). These are part of the life cycle 

 of the fungus and nppear to be chlamydospores comi)arable with those 

 of Hyponn/res solani described by Keinke and Berthold.' They api)ear 

 to have an outer and inner wall and germinate readily in water, but 

 have not been studied as critically as the other spore forms. They 

 were found in many test tube cultures, and have been observed a num- 

 ber of times on the surface of the dead stems associated with the macro- 

 conidia. They are usually 10 to 12 /.i in diameter, the extreme limits 

 of those measured ranging from 7 to 15 ii. 



(4) Pyc7iidia{.^).—^o pycnidia have been seen either on the host plants 

 or in any of several hundred cultures made on a great variety of media. 

 The cultures began in the summer of 1894 and are still in progress. 

 The examinations on the host plants have included hundreds of dying 

 and dead specimens collected in diflerent years and in various locali- 

 ties from July to October. From these observations the writer believes 

 he is warranted in concluding that there are no pycnidia in the life 

 cycle of this fungus. 



EFFECT OF MODIFICATIONS OF THE SUBSTRATUM. 



The effect of modifications of the substratum on (1) the production 

 of a stroma, (2) the color of the mycelium, (3) the color of the perithe- 

 eia, and (4) the development of the peritheeia, is described ill the 

 following i^aragraphs: 



(1) The production of a stroma. — The insignificant subiculum on the 

 host plants and the thick stroma on potato have already been con- 

 trasted. Tlie limits of the stroma on potato are beautifully differen- 

 tiated when thin cross sections are put into chlor-iodid of zinc. The 

 starch-bearing cells of the substratum become blue, while the stroma 

 becomes yellow, and the exact limits of fungus and substratum are 

 easily distinguished. On ordinary nutrient agar the cowpea fungus 

 produces only a feeble stroma. The addition of 1 per cent cane sugar 



' Die Zersetzung der Kartoffel durcli Pilze. 



