CH. ii.] CLOVER SICKNESS CLOVER MILDEW. 7 



cidium medicaginis, Desm., has also with, insufficient reason 

 been referred to as the cause of the disease. It is almost 

 impossible to say what may be the chief cause of clover 

 sickness, and there may be several forms of the disease. 

 The spawn of fungi is sometimes confined to the interior 

 of plants, where it causes serious disturbance, and this 

 spawn or mycelium, if without fruit, even when seen 

 under the microscope, is commonly so indefinite in char- 

 acter that no one can say for certain what fungus it is 

 destined to produce. 



A frequent fungus on dying clover leaves is Ascdbolus 

 trifolii, Biv., which is the same with Phacidium trifolii, 

 Boud.; and another is Polythrincium trifolii, Kze., which 

 is said by some authors to be a second condition of Do- 

 thidea trifolii, Fr. A rust fungus named Uromyces append- 

 iculata, Lev., is also at times very prevalent on the pea- 

 flower tribe. The fungus parasites of the Leguminosce, to 

 the pea-flower tribe of which our clovers belong, are but 

 few in number, although their individual power for de- 

 struction is great. The best known are the mildews of 

 our garden and field peas named Erysiphe Martii, Link., 

 and E. communis, Schl., the latter of which also occurs 

 upon the Ranunculacece and the vine. A close ally named 

 E. graminis, D.C., is parasitic on grasses. 



A very frequent parasite of clovers in Britain, and one 

 to which we are inclined to refer a great deal of clover 

 sickness, is Peronospora trifoliorum, D.By., a pest which 

 appears to have attracted little or no attention in this 

 country till late years. 



It, like all other species of Peronospora, attacks living 

 plants ; it is common on purple clover, Trifolium medium, 

 L. ; T. alpestre, L. ; crimson clover, T. incarnatum, L. \ -on 

 Lucern, Medicago sativa, L., and other plants. There is 

 some diversity of opinion as to the meaning of the name 

 Peronospora, as Corda, the botanist who first used the jname, 

 gave no explanation of its derivation. Corda probably 

 had in view the word peronao (Tre/oovaw Homer and 



