A Study of Meadow-Crop Diseases in New York 69 



as well as from the poor stands that result from low germination of seed 

 from diseased plants (Dickson and McRostie, 1922:42). McLarty (1920: 

 503) says of sweet-clover mosaic that " when growing wild, diseased plants 

 3'ield about one-half the herbage of their healthy neighbors." In Penn- 

 sylvania, C. R. Orton found a six-and-one-half-acre field of crimson clover 

 in which 50 per cent of the plants were diseased (Johnson and Haskell, 

 1920). Mains (Kirby and Archer, 1927:199) reports a 0.5 per cent loss 

 for Indiana in 1926. 



Symptomatology 



To any one who is acquainted with mosaic on other plants, the symptoms 

 of this disease on clover will be familiar. The usual mottled, crinkled, 

 and curled leaves are very evident, as illustrated in figure 16. Frequently 



Figure 16. mottling and wrinkling of leaves of red clover results from infection 



by mosaic virus 



the size of the leaf is more reduced than that shown in the photograph. 

 The crinkling is due to an unequal rate of growth between the diseased and 

 healthy tissues, as pointed out by Dickson (1922 b: 14). Another hypo- 

 plastic symptom is shortening of internodes which, with the dwarfing of 

 the leaves, may at times reduce the size of the plant a half. The 

 inflorescence also is reduced considerably with attendant small yields of 



Seed. 



Dickson (1922 b:45) states that, "Leaf thickness in [diseased] red 



clover varies from 105 microns in the lighter to 150-180 in the darker 



Chloroplasts are fewer and paler in the lighter areas and the intercellular 



