446 MR. A. J. EWART ON ASSIMILATORY INHIBITION. 
the assimilatory cells against those rays of light which under 
intense and prolonged exposure tend to induce in the plasma, 
more especially of the chlorophyll grain, a condition of light 
rigor, and thereby diminish or inhibit their power of assimilation. 
Assimilation in Parasitic Plants with Normal or Modified 
Chlorophyll. 
Bonnier * has recently worked on the assimilation of green- 
root parasites as exemplified among the Scrophulariacee, and 
finds that Melampyrum can assimilate 2, Pedicularis and Rhinan- 
thus 1, and yellow-green individuals of Rhinanthus and Bartsia 
only +); the amount of CO, that the non-parasitic Veronica can. 
In the last case it is only under strong illuminaticn that assimi- 
lation is greater than respiration, whilst in Euphrasia and in 
some plants of Rhinanthus and Bartsia, even by strong illumi- 
nation, no evolution of oxygen can be detected. The mere fact, 
however, that the power of assimilation is much less active in 
one plant than in another from an allied genus is by no means a 
sufficient proof that the former plant obtains a portiou of its 
carbohydrates parasitically, but may be simply due to the fact 
that the amount of carbohydrate material consumed or required 
is less in the former case than in the latter. The yellow-green 
individuals of Rhinanthus and Bartsia, which have almost no 
power of assimilation, and in which almost complete parasitism 
1s supposed to exist, are inan abnormal condition, and are not fit 
subjects for experimentation. As regards Euphrasia, Bonnier is 
certainly in error. The chlorophyll grains of this plant are large, 
green, and normal, and all living ehlorophyllaceous cells, not only 
in Euphrasia officinalis but also in Rhinanthus Crista-galli and 
Bartsia Odontites, show, on examination by the Bacterium method, 
an active power of assimilation. 
Bonnier’s error may arise from the fact that the cut plants 
kept with their stems in water are very liable to be injuriously 
affected. Thus after 6 hours’ exposure to full sunlight quite 
unwilted plants show no perceptible or only a very weak power 
of assimilation, which is, however, after a night in darkness, 
again present and fairly active in all living leaves. If the plants 
* Bonnier, “Sur assimilation des plantes parasites à chlorophylle," in 
Comptes-rendus, Paris, 1891, t. cxiii. p. 1074. 
