46 

 i 



appears usually, on the upper leaves and causes them to curl 

 and die. The flower-spike instead of ripening the usual quantity 

 of seed forms a bushy, leafy, mass and bears no seed at all. 

 The fungus has kept a great many plants of this weed from 

 "going to seed" this year. 



PL ASM or A MA HALSTEDU, ( Farl. ) BerL and DeToni. On leaves 

 of wild artichoke (Helianthus tnberosus), and marsh elder 

 (Iva xanthi folia). Plentiful. This is the most destructive 

 species of my acquaintance. Many plants were found with 

 every leaf affected. The marsh elder is one of our commonest 

 roadside weeds, and thousands of them were killed this sea- 

 son by the mildew. July September. 



CYSTOPUS JJLITI, (Biv. ) DeBary. White rust of pigweed. Very 

 plentiful on common pigweed (Amarantus retroflexus), and 

 the tumble weeds (Amarantus alba and A. blitoides). It 

 forms white patches on the under side of the leaves; which 

 break open later emitting many white, powdery, spores, hence 

 the name "white rust." Quite injurious especially to the 

 tumble weeds. July October. 



CYSTOPUS < ANDIDUS, (Pers.) Lev. This white rust occurs upon a 

 great number of hosts belonging to the order Cruciferae. It 

 has been collected 011 pepper grass (Lepidium virginicum 

 and L. intermedium), hedge mustard (Sisymbrium offi- 

 cinale), shepherd's purse (Capsella bursa-pastoris), black- 

 mustard (Brassica nigra), white mustard (B. abla), charlock 

 (Z>. arvemis), and water cress (Nasturtium hispidum). 



CYSTOPUS portulacae, (DC) Lev. White rust of purslane. Af- 

 fects the under side of the leaves of purslane (Portulaca ole- 

 racea). Very plentiful but apparently doing little damage. 



CYSTOPUS TRAGOPOGONIS, (Pers.) Schroet. On rag weeds (Ambrosia 

 spp.\ Common. By far the most destructive species of this 

 genus, comparing well with Plasm, kalstedii. In many places 

 aloii^ the roadside and streets the weeds were completely 

 stripped of all but the very uppermost leaves, and sometimes 

 even these succumbed. What is probably the same species 



