514 



LECTURE XXX. 



little wood, and that this wood is soft. The stem of such a shaded plant may be 

 easily cut through with a pocket-knife, though this is not the case with a normally 

 grown plant of the kind mentioned above, on account of the hardness of the wood. 

 I have already mentioned in a previous lecture and in another connection that the 

 so-called laying of wheat when it grows too rank is due to the shading of the lower 

 joints of the haulm, and its deficiency in sclerenchyma. 



We have already become acquainted with a particularly fine and instructive 

 example of the influence of chlorophyll on the whole mode of growth of a plant, in our 

 previous considerations on the nutrition of the Lichens. We found that the Lichens 

 are true Fungi (Ascomycetes) and nevertheless their bodies have in general forms 

 quite different from those of all other Fungi. All that appears above the substratum 

 in the case of ordinary Fungi is usually a fructification; the Lichens on the contrary 

 are developed entirely outside the substratum, or they send their root-hairs only into 

 it. The body of the Lichen, instead of showing a tendency to the formation of 

 thick fleshy or even woody masses, as other Fungi, assumes either the form of 

 thin leaf-like expansions, or bands, or thin much-branched shrubby structures. 

 In other words, the tendency prevails among the Lichens to assume the form of 

 ordinary plants with flat extensions or branched filiform structures, and this, as I 

 have already said, is solely in consequence of the fact that the tissue of the Lichen- 

 fungus encloses Algae, which contain chlorophyll and look as if they constituted 

 a normal anatomical constituent of its tissue. This, however, is equivalent to 

 saying that since these chlorophyll-cells are simply for the purpose of assimilating 

 they must be presented to the light in thin but relatively extensive surfaces, and 

 this is accomplished in the case of the foliaceous Lichens just as in ordinary 

 foliage-leaves, and in the fruticose Lichens just as with leafless shrubs, where the 

 assimilating tissue is situated in the external cortex. If the correlation between 

 chlorophyll and the whole growth of a plant comes out clearly at all, it is certainly 

 in the comparison of the forms of Lichens with those of the bodies of other Fungi. 

 Here we have to a certain extent the test for what I have said concerning the 

 correlation between chlorophyll and the configuration of the plant generally. 



