374 



LECTURE XXIII. 



of the stem of a Linum attacked by it disappears when a haustorium penetrates 

 into the cortex ^ 



In the case of phanerogamic humus plants which contain little or no chlorophyll, 

 (Neottia, Corallorrhiza, Epipogon, Monolropa, Lathraa, etc.), the relations referred to 

 are not so clear as in the case of the parasites. Although there can be no doubt 

 that these plants take up the whole of their organic substance, or at any rate the 

 greater part of it, from the humus remains of the soil surrounding them, special 

 haustoria are nevertheless not known at all in these plants. . Even in Neottia, the 

 relatively small length and number of the roots is noticeable, and in Corallorrhiza 

 they are entirely wanting. In these cases the root-hairs which spring from the roots 

 or subterranean shoot-axes appear to serve as haustoria, which are connected with 



the still unrotted remains of fallen 

 leaves or other humous substances; 

 and which excrete ferments to dis- 

 solve them and absorb the pro- 

 ducts of solution. The generally 

 very slow increase in mass and 

 vigour of such plants accords 

 with this incomplete arrangement. 

 With respect to the absorption 

 of organic nutritive materials, the 

 so-called 'Insectivorous Plants' 

 are better known than the true 

 parasites and humus-plants. The 

 striking adaptations which pro- 

 mote the absorption of organic 

 substance in them have for many 

 years astonished a large number of 

 observers and led them to active 

 investigation. It appears to me 

 that in the case of the insectivorous 

 plants we meet with a remarkable 

 case where nature has contrived 

 complicated mechanisms for the 

 attainment of an extremely unimportant eflFect ; for although it cannot be doubted 

 that the small quantities of proteinaceous substance which the insectivorous plants 

 absorb from animal bodies are useful for their welfare, the contrast between the com- 

 pUcated adaptations to this end and the evidently very small amount of biological work 

 which they perform is nevertheless, on the other hand, very striking. Moreover, it is 

 certainly not doubtful that just the most pronounced insectivorous plants, as Nepenthes 

 and Dionma, can also thrive continuously without this occasional supply of organic 

 substance. With respect to the absorption of nutritive matters by true parasites 



Fig, 245. — Riciniis communis. J ripe seed in longitudinal section ; 

 // seedling the cotyledons of which are still m the endosperm — com- 

 pare A and B ; s testa ; e endosperm ; c cotyledon ; he hypocotyl ; w 

 primary root ; w' its lateral roots; xan appendage of the seed peculiar 

 to Euphorbiacea:. The endosperm increases during germination in 

 proportion as the seedling-leaves which it envelopes : it is at length 

 absorbed entirely by them and the remains cast off. 



^ I established exactly the same line of thought as that in the text, in my ' Handbuch der Experi- 

 mental-physiologie,^ 1865 (§ 55, p. 192). This statement, depending on careful investigations, appears 

 however to have been completely overlooked by more recent writers who have been concerned with 

 the absorption of organic substance by plants, as Pfeffer, Darwin, Drude, and others. 



