DISEASES OF TRUCK CEOPS. 45 



dead, while those higher up on the phmt were chlorotic either en- 

 tirely or in part. Such leaves are copiously dow^ny white on the 

 lower surface. This disease was very abundant in a truck garden, 

 the only place where it was observed. 

 Specimen collected: Austin, 3040. 



Powdery mildew {Erysiphe folygoni DC). — This fungus causes 

 the characteristic white appearance of the leaves, which at length 

 become yellow and dry. 



Specimen collected: Cotulla, 2930. 



WATERMELON. 



Blossom-end blight and rot. — A very common and destructive disease 

 of the watermelon {Citrullus vulgaris Schrad.) is characterized by 

 the blighting and atrophy of the blossom end of the fruit followed by 

 the rotting of the entire fruit. The blossom end turns brown, dries 

 more or less, and remains smaller than the remainder of the fruit. 

 (PI. X, fig. 1.) The trouble may begin very soon after the blossom 

 stage and the affected fruit may never reach any considerable size, 

 or the trouble may begin later and the fruit may reach nearly normal 

 size before it is destroyed. In some cases observed it was impossible 

 to find any fungus present in the blighted portion, but in the majority 

 of cases the fruit was invaded by a Fusarium which transformed the 

 melon into a soft, rotting mass. 



The Fusarium present comes to the surface on the side of the 

 melon in contact with the soil, and in specimens kept in a damp 

 atmosphere conspicuous pinkish spore tufts are produced over the 

 surface. Only macroconidia, 18 to 24 by 3 /a, falcate, and two septate, 

 have been observed. 



The definite etiology of this disease is not known, and it can only 

 be suggested that the blighting is due first to the excessive transpi- 

 ration at times when root activity is not sufficient to meet the loss, 

 and that the fungus gains an entrance into the dead tissue and then 

 spreads throughout the remainder of the fruit. 



This is the most serious trouble of the watermelon and is gener- 

 ally prevalent. The loss may be from 25 to 75 per cent in many cases. 

 The very general prevalence of this disease is such that a more de- 

 tailed investigation should be undertaken. 



Specimens collected: New Braunfels, 1G90; Austin, 1870; Beeville, 1817 

 (collections do not represent the prevalence). 



leaf-spot {Cercospoi'a citrullina Cke.). — The oldest leaves of the 

 plant are the first to show these circular spots, 2 to 4 mm. in diameter. 



226 



