F. J. F. SHAW 121 



which might be present. As, however, the conditions necessary for the germi- 

 nation of the seed of parasites such as Orobanche are known to be delicate, 

 it was not considered advisable to sterilize all the pots. In all 92 pots were 

 used of which 36 were planted with tobacco, 24 with mustard, 16 with turnip 

 {Brassica campestris var . rapa) and 16 -with cabbage. Those pots were 

 then infected with seed of 0. cermia and 0. mdica which had been 

 collected in the season 1915-16, In the case of 0. cemua the seed used had 

 been collected from three distinct sources — from plants which were parasitic 

 on tobacco, from plants which were parasitic upon tomato and from 

 plants which were parasitic upon brinjal {Solanum Melongena Liiui.) In 

 the case of 0. indica the seed used was obtained from four sources, 

 namely, from plants parasitic respectively upon cabbage, mustard, turnip, 

 and tobacco. For convenience in this account the particular kind of seed 

 of OrohancTie is indicated by the addition of the name of the host plant, 

 from which it was collected, after the specific name ; thus seed 0. indica 

 cabbage means seed of 0. ^wt^zm collected from plants parasitic upon cabbage. 

 In this way it was hoped to observe whether the influence of the previous host 

 had any effect upon the parasitism of the seed of either 0. cemua or 0. indica. 

 The number of pots sterilized was 16, and 46 pots received each 1 oz. of 

 sodium nitrate when the host plants were well established. These details are 

 apparent in the Hst of the pots (page 123) and in the plan of the experiment. 

 (Text-figuie 7.) 



Seed 0. cemua tobacco was infected upon four pots each of tobacco, mustard, 

 cabbage, and turnip. This was done by scattering a quantity of the seed on 

 the surface of the soil and mixing lightly with a small stick. In the case of 

 tobacco and cabbage the host plant had been planted in the pot some days 

 previously ; in the mustard and turnip pots the seed of the parasite was sown 

 mingled with that of the host. Half of the pots had received 1 oz. each of 

 sodium nitrate. After about six weeks (from November 8th to 15th) plants 

 of 0. cemua appeared in three of the tobacco pots and considerably 

 later (2nd January) also in the fourth pot of tobacco. Those pots which had 

 received nitrate were indistinguishable, except in regard to the development 

 of the host, from the others. No plants of 0. cemua appeared in the pots of 

 mustard, cabbage, or turnip. Late in January, when the pots had been 

 standing in the open for four months, a few plants of 0. indica appeared in one 

 pot of cabbage and three pots of turnip. The time at which they appeared, 

 coupled with the fact that they were not of the species of Orobanche used in the 

 infection, indicates that their origin is to be attributed to chance infection 

 by air-borne seed after the experiment was started. 



