i88 METABOLISM 



on to others of the same species, as L. KOCH (1888) was the first to show, 

 and that one of several seeds bound together by haustoria develops at the 

 expense of the rest. 



HEINRICHER, to whom we owe exhaustive researches on the Rhinantheae 

 (i897,onwards) has endeavoured to prove that these parasites decompose carbon- 

 dioxide by means of chlorophyll in the normal way. This cannot be proved 

 with certainty, and researches are especially wanting as to whether the pro- 

 ducts of assimilation so formed are quantitatively sufficient for their needs 

 (compare what has been said above as to Cuscuta). It is possible that the chloro- 

 phyll function may be present but in a weakened form, that it is insufficient for 

 the plant's requirements, and that the plant must have recourse to ready formed 

 carbohydrate. On the other hand, one may explain the parasitism of these plants 

 by saying that they are dependent on their hosts only for nitrogenous material, 

 perhaps in the form of proteid or amide bodies, or for the materials of the ash. 

 HEINRICHER, on account of the quantity of nitrates in parasites, decides in 

 favour of the latter possibility and concludes that these green parasites employ 

 their hosts as a source of unelaborated sap only. The question is a purely 

 experimental one and the decision will depend on the results of such experi- 

 ments. 



The common mistletoe is still imperfectly known so far as the physiology 

 of its nutrition is concerned. Owing to the fact that the union between host 

 and parasite is limited to the water-carrying vessels, we are led to believe that 

 Viscum takes only water and inorganic salts from its host ; and such a relation is 

 more probable in a plant that lives high up on trees than in forms like Euphrasia, 

 which has roots in the soil and is partly, at least, provided with roothairs. 

 Viscum may be conceived as a plant, originally epiphytic, which has surmounted 

 the difficulty of the deficiency of water and salts against which most epiphytes 

 have to contend by attaching itself to the vascular systems of other plants. 

 This conception has not, however, been substantiated, and here also experi- 

 mental research is necessary. 



Exhaustive morphological and developmental studies on these interesting 

 phanerogamic parasites are to be found in the following works : 



Orobanche : KOCH (1887) ; Lathraea : HEINRICHER (1895) ; Cuscuta : 

 KOCH (1880), PEIRCE (1894). 



Rhinanthaceae : KOCH (1889 and 1891), HEINRICHER (1897, 1898, 1901) ; 

 Loranthaceae : PITRA (1861). 



The difference between autotrophic and heterotrophic plants, it must once 

 more be clearly pointed out, lies solely in the mode of absorption of nourish- 

 ment, and consequently we may speak of unicellular green organisms 

 only as autotrophic, for there the whole plant is concerned ; on the other 

 hand, in the case of the higher plants only certain parts are autotrophic, the 

 leaves especially, whilst others, as, for example, the roots, are completely 

 heterotrophic. So far as regards the further alteration of the organic com- 

 pounds of carbon and nitrogen, it is quite immaterial whether these are used 

 for constructive purposes in the regions where they are made or whether they 

 be translocated in an already prepared condition. There is no essential 

 difference between the metabolism of heterotrophic and of autotrophic forms. 



As in green plants, so in Fungi, the nutritive substances are employed in 

 the construction of the body, are stored in reserves or, when of no more use, 

 are transformed into waste products ; that is to say, we have here also to 

 distinguish (i) plasta ; (2) reserves ; (3) translocatory materials ; (4) excreta. 

 On the whole the cell of the fungus is constructed out of the same kind of materials 

 as that of the Phanerogam, and although there are deviations in individual cases, 

 e. g. in the occurrence of chitin in their cell-walls, still we need not go further 

 into the matter, since, both in these as in the higher plants, we are unacquainted 

 with the conditions of origin of the different constituents of the cell. The 



