368 LECTURE XXIII. 



devoid of chlorophyll, as presenting the typical case of the absorption of organic 

 substance. It is at once conspicuous that in the life of these plants it is by 

 no means simply a matter of the want of chlorophyll, and the compensation 

 of the chlorophyll-function by the absorption of organic substances : on the 

 contrary, the internal causal interdependence of all vital phenomena involves that 

 the vv'hole internal and external organisation of plants devoid of chlorophyll should 

 deviate essentially from the normal. I have already, in Lectures III and V, 

 referred in this sense to the organographical peculiarities of parasites and sapro- 

 ph)ftes, and laid special stress on the fact that with the absence of chlorophyll the 

 presence of large transpiration surfaces would be superfluous, or even injurious, and 

 that therefore plants devoid of chlorophyll possess no large leaves, and for the same 

 reason they form no true wood. Where plants devoid of chlorophyll tend to the 

 formation of more vigorous vegetative and reproductive organs, these are never 

 conspicuous for their superficial development, but, on the contrary, for their small 

 superficies and relatively large mass. Nutrition by the absorption of organic 

 substance thus reacts on the whole organisation of the plant. No single plant 

 devoid of or containing but little chlorophyll possesses the ordinary habit, and least of 

 all the large leaves and surface development and slender growth generally, of normal 

 plants. This is so far the case that every one, even those unfamiliar with botanical 

 matters, recognises in the parasites and saprophytes devoid of chlorophyll organisms 

 of peculiar structure. No other biological condition effects a change in plants so 

 deeply affecting the whole organisation as does the want of chlorophyll and the ab- 

 sorption of organic substance. This goes so far that even the reproductive organs 

 are influenced by it and degraded to a great extent : all plants devoid of chlorophyll, 

 even when they are descended from highly organised types of Phanerogams, are 

 remarkable for their exceedingly small, often almost microscopic seeds, and the 

 embryos in these seeds often consist of only a few cells, and are not segmented 

 externally. In the Rafllesiacese, Balanophoreae, Orobanchaceae, and Monotropa, 

 the embryos have no trace of radicle and plumule, and in the Cuscutese there is 

 only a feeble indication of such. 



Parasitism, moreover, works not only to the degradation and alteration generally 

 of the organisation of the parasite itself, but the living plants attacked by the parasite 

 are altered by it. In the first place, it is clear that the withdrawal of a certain 

 quantity of plant-substance, which the parasite puts in requisition for itself, must 

 enfeeble the host-plant ; and in many cases this goes so far that the latter is prevented- 

 by feebleness from concluding its life in the normal manner. This is the case, for 

 example, when numerous specimens of Orohanche speciosa attach themselves to the 

 roots of Vicia Fdbia. In other cases, however, the effect on the host-plant goes 

 further. The parasite induces phenomena of irritability on the part of the host-plant, 

 bringing about vigorous local growth — for example, the active wood-formation and 

 production of tuberous swellings in woody plants attacked by Viscum. or Lorcm- 

 thus EuropcBus, and many Fungi inhabiting wood, cause the formation of resin in 

 Conifers, and injure the latter in consequence (Robert Hartig). But even the normal 

 processes of configuration of the host-plant may be rendered abnormal by parasites. 

 For -example, the ligneous bundles of the roots of the host on which Balanophora is 

 parasitic grow into the tuberous vegetative body of the latter, and serve to a certain 



