272 



THE FUNGI WHICH CAUSE PLANT DISEASE 



spores elliptic, hyaline, rarely curved, 12-20 x 5-8 n; paraphyses 

 long and slender, very abundant. 



Conidia (=Colletotrichum gossypii), acervuli erumpent, coni- 

 diophores colorless, longer than the spores, 12-28 x 5 m; conidia 

 irregularly oblong, hyaline or flesh-colored 

 in mass; setae single or tufted, dark at base, 

 colorless above, straight, rarely branched. 

 The conidial stage of this fungus was de- 

 scribed by Southworth ^^' ^" and independ- 

 ently by Atkinson ^^' '''• '^ on cotton. 



The ascigerous stage was first seen by 

 Shear & Wood ^^ in artificial culture and by 

 them regarded as probably a variety of G. 

 rufomaculans. Since these studies Edger- 

 ton^ from examination of perithecia de- 

 veloped naturally in the open, has proposed 

 it as a separate species. 



The mycehum is richly branched and sep- 

 tate, usually hyaline but sometimes slightly 

 Fig. 201.-G. gossypii. ^moky. It grows between and in the host 

 Secti9n of young boll, cells which are often filled with it, causing 

 penetrating the huU coUapsc, loss of chlorophyll, and browning. 

 young "sL"'°lporeI Studies by Atkmson and by Barre ^ show 



are being produced that in case of diseased bolls the mycelium 



upon the outer por- " . 



tion of the hull and may extend through the pericarp, spormg on 



upon the surface of ., . ii _l j iu j. it, j 



the young seed coat, its inner wall; extend tnence to tne seeds; 



After Barre. penetrate and grow in them, Fig. 201, and in 



the cells of the lint. Barre has shown that even the endosperm 

 and cotyledons may be invaded, Fig. 201, and spores produced 

 upon them while within the seed coats. Such seeds and lint may 

 appear outwardly as though perfectly normal. 



The conidia are formed in acervuU, subtended by stromata. 

 Setae, from few to many increasing with age of the acervulus, 

 are present and conidia are occasionally found on them. In ger- 

 mination conidia usually develop one, sometimes two septa and 

 produce dark chlamydospores. Acervuli are common on bolls, 

 less so and smaller on leaves and stems. 



The perithecia as found in the field by Edgerton in Louisiana 



