278 DISEASES OF CULTIVATED PLANTS 



lucerne (Medicago sativa\ and as the disease spreads very 

 quickly the entire crop usually suffers. The leaves are 

 attacked, the injury first appearing as numerous minute spots 

 which show both on the upper and under surface. At a later 

 stage the ascophores burst through the skin of the leaf under 

 the form of minute pustules or warts. 



Ascophores produced in small groups on the upper surface 

 of the leaf, dingy yellow, about 0*5 mm. across; asci clavate, 

 8-spored ; spores hyaline, elliptic-oblong, 10-15x5-6 /x ; 

 paraphyses rather stout This fungus has also been called 

 Pseudopeziza medicaginis (Sacc.), P. divergens (Sacc.), and 

 Phacidium medicaginis (Lib.). 



When the disease is observed it is advisable to cut the crop 

 frequently ; by adopting this method the forage is saved, 

 otherwise all the leaves are lost, and fall to the ground carry- 

 ing the fungus along with them, thus endangering a future 

 crop. In America diseased fields are burnt over during the 

 winter or early spring. If there is not a sufficient quantity of 

 dead material present, a sprinkling of straw or some dry litter 

 is used. This method removes all dead, infected material 

 lying on the ground. The fungus is parasitic on wild clover, 

 medick, etc., and these are consequently a source of danger. 



Currant leaf spot. This disease was at one time attributed 

 to Gloeosporium ribis (Mont.), which was considered as an 

 entity ; it is now considered by Klebahn to be nothing more 

 than a stage in the life-cycle of an ascigerous fungus which he 

 has named Pseudopeziza ribis. The Gloeosporium condition, 

 however, appears able to reproduce itself continually without 

 the intervention of the ascigerous form, which has not yet 

 been recorded in this country. 



The Gloeosporium stage often does serious injury to the 

 leaves of gooseberries, black and red currants, and also other 

 introduced kinds of Ribes. The disease spreads rapidly, 

 causing the leaves to fall early in the season. This not only 

 checks the growth of the fruit already present, but also 

 influences the crop for the following season. The first indica- 

 tion of injury usually appears just about when the leaves are 

 full grown, under the form of small blackish spots, principally 

 on the upper surface ; these spots are dense masses of 

 mycelium in the tissue of the leaf, from which originate the 

 spore-clusters that eventually rupture the epidermis of the 

 leaf, allowing minute, oblong, curved spores, 10-12x5-6 /^, 



