Dorothy M. Cayley 475 



latter enables the plant to attain sufficient maturity before external 

 conditions are conducive to the rapid development of the organism. 



Thanks to the courtesy of Mr F. J. Chittenden, I was able to examine 

 a large number of different varieties of early peas grown at the Wisley 

 Early Pea trials in 1915. The plants had all but ripened off, and only 

 one variety was found which showed the typical discoloration of the 

 cotyledons, although, judging from external appearances there were 

 many doubtful cases. A row of Duke of Albany, growing in an adjacent 

 plot but in a much earlier stage of development, showed the typical 

 discoloured patch in the centre of the cotyledons. 



It must, however, be pointed out that the disease is not so prevalent 

 at Wisley as it was at this Institution, and that the trials, so far as the 

 disease is concerned, cannot be taken as giving conclusive results. But 

 general observations on pea plants grown on soil known to be infected 

 illustrate this point much more conclusively. There is also the possi- 

 bility that, in the two cases in point, of diseased varieties occurring at 

 Wisley the disease may have been introduced with the seed, as it is 

 impossible to tell from the external appearance whether a seed is healthy 

 or diseased. It can thus be seen that it is very difficult to get results 

 which are really reliable. 



Of the dwarf succulent early varieties Chelsea Gem and Little Marvel, 

 and of the later varieties Ne Plus Ultra and Duke of Albany, are par- 

 ticularly susceptible. Sugar peas and rogue peas can also become 

 badly diseased when grown on infected land. 



It is hoped, after further trials, that it may yet be possible to find an 

 immune variety, so that by breeding this immunity may be transferred 

 to some of the excellent varieties of culinary peas already on the market, 



Eemedies. 



So far no cure is known : in fact, a cure is hardly possible in this 

 case of a succulent annual, especially when the seed itself may be in- 

 fected with the parasitic organism. The precautions to be recommended 

 are the rotation of crops, early sowing, and general healthy cultural 

 conditions as to drainage, sufficiency of lime, etc., and the rejection, 

 where possible, of seeds known to have come from diseased plants. 

 The haulms from an infected crop, together with the sticks, should 

 be burnt as soon as possible after the crop has been gathered. Partial 

 sterilisation of the soil is useless, as Ps. seminum is a sporing 

 organism ; it is also impracticable owing to the amount of labour required 



