128 OROBANCHE AS A PARASITE IN BIHAR 



" tokra " before its seed has ripened. In this connection it may be mentioned 

 that the practice of taking a second cut from the tobacco is a bad one ; the 

 longer the tobacco is kept in the soil the more " tokras " come up and the 

 more seed is matured to hifect the soil for the next crop.' 



It is evident that the parasitism of 0. indica is much more complicated than 

 that of 0. cernua. 0. cernua is practically restricted to solanaceous crops ; in 

 all the thousands of " tokra " counted only four specimens of 0. cernua were 

 found upon mustard. 0. indica has, however, a much wider range of hosts as 

 is evident from a glance at the list (page 130). Field observations suggested, 

 and pot culture experiments have shown, that in 0. indicath^Te are at least 

 tw^o races, one of which is parasitic upon tobacco and does not attack 

 mustard, while the other is parasitic upon mustard, turnip, and cabbage and 

 does not attack tobacco. It has been proved by other investigators^ that 

 the seed of some phanerogamic parasites (e.g. Orobanche, Tozzia) will not 

 germinate except in the presence of the appropriate host. If the conditions 

 for the germination of the seed of such parasites are so delicately adjusted 

 to their environment it is not surprising to find that in a morphological 

 species such as 0, indica, differences in parasitic quality may exist without 

 accompanying morphological distinctions. 



In this connection the scarcity of 0. indica in the second season indicates 

 that the slight climatic differences between two successive cold seasons may 

 have a powerful influence in determining the amount of this parasite, and 

 Beck von Mannagetta considers that some species, notably 0. cetniia, have 

 shown marked morphological variations in their epread to regions of different 

 climates. 



Plants such as Orobanche have always attracted a good deal of attention 

 from botanists. One of the earliest works on this genus appears to be that of 

 Vaucher^, who gives a list of parasitic species and their hosts and made some 

 observations on the germination of 0. ramosa upon Cannabis saliva. This was 

 probably one of the first attempts to grow Orobanche in cultures. The biology 

 and anatomy of the genus was very extensively studied by Kcch*, the 

 later monograph of Beck von Mannagetta^ being rather from a systematic 



1 Howard, A. and G. L. C, "Tobacco cultivation in Bihar.'" Agri. Res. Institute, 

 Pusa, Bvll, No. 50, 1915. 



2 Heinricher, E., Die Avfzucht und kultur der Parasitischen Samenpflanzen. Jena, 1910. 



3 Vaucher, J. P., Monographie des Orobanches, Paris, 1827. 



* Koch, L., Die Entwicklungsgeschichte der Orobanchen, Heidelberg, 1887, 



' Mannagetta, Beck von., loc cit., page 108. . _- 



