64 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Physiology. 

 Nutrition and Growth. 



Parasitic Flowering Plants.* — A. Fraysse contributes a summary 

 of his recent papers dealing with the biology of parasitic Phanerogams. 

 The genera examined include Osyris alba, Gytinus Hypocistis, Odontitis 

 rubra, Euphrasia officinalis, Lathrma squamaria, L. clandestine,, and 



Mtiiwtropa Hypopitys. 



The author finds that the plants most readily attacked by such 

 parasites as Lathnea, Euphrasia, etc., winch attach themselves by 

 suckers, are those with bacteria-nodules, tubercles, mycorhizas, etc. 

 The suckers are sometimes pericyclic, sometimes endodermic in origin, 

 and probably represent modified roots. The invasion of the parasite 

 usually causes the formation in the host of a cambium zone, a layer of 

 cork or other similar structures for the purpose of isolating the infected 

 region. There may also be much mucilage or gum formed around the 

 point of attack. Some of the green parasites absorb both mineral food 

 and carbon compounds from their hosts, e.g. Odontites, while others only 

 absorb carbon compounds, e.g. Euphrasia. Those without chlorophyll 

 absorb the whole of their food from the host. In all cases, the parasite 

 has a selective power, and by means of diastases converts the absorbed 

 food-materials into compounds suitable for assimilation. Glucose 

 appears to be the principal source of carbon, and thei'e is a special 

 diastase present for converting the starch of the host-plant into this 

 sugar. The latter may be immediately assimilated, or may be absorbed 

 and then reconverted into a form of starch until needed. Tannin may 

 be used, as in Gytinus, as an agent of nutrition and protection. The 

 suckers contain substances which protect the parasite from the toxins 

 secreted by the host. Infection is effected by the agency of cellulose- 

 diastases, and other ferments of a similar character, which are most 

 active when the host offers the greatest resistance. 



Parasitic Phanerogams and Nitrates. f — M. Mirande has con- 

 ducted experiments with the view of discovering whether parasitic 

 phanerogams absorb nitrates. The method employed was that of quali- 

 tative analysis of the plant-sap by microchemical methods, using the 

 sensitive sulphuric-diphenylamine reaction, and special attention was 

 given to the organs of attachment, roots, suckers, etc. Parasites with 

 little or no chlorophyll do not absorb nitrates from the host-plants, 

 semi-parasites may or may not absorb nitrates. It appears that the 

 reduction of nitrates depends upon the chlorophyll-function, and hence 

 those plants which are destitute of chlorophyll, and thus unable to 

 reduce nitrates, absorb nitrogen from the host-plants in a state of 

 organic combination, thus profiting by the chlorophyll-function of the 

 host-plants. Variation in the power of nitrate-absorption fluctuates 

 with the amount of chlorophyll present. 



* Rev. Gen. Bot., xix. (1907) pp. 49-69 (13 figs.). 

 t Coniptes Rendus, cxlv. (1907) pp. 507-9. 



