64 



LECTURE V. 



parasites of this kind which protrude, from the substratum have, in comparison with 

 the typical shoots of the vascular plants, something uncommonly strange about them. 

 They sometimes resemble in their whole aspect the fructifications of large Fungi ; 

 in a very striking manner, for instance, in the genus Scyhalium. That in all the 

 saprophytes and parasites hitherto mentioned, it is in fact only the want of chloro- 

 phyll by which the degradation of all the vegetative organs has been brought about, 

 is clear at once, if we compare with them the Misletoe and the whole family of the 

 LoranihacecB. These plants also are parasitic by their roots, as has already been 

 shown, on the tissues of their host-plants. They are, however, abundantly provided 

 with chlorophyll, and accordingly their shoot-formation leaves nothing to be desired. 

 Their broad, dark green foliage leaves, on green, sharply segmented axes, possessing the 

 anatomical structure of highly organized vascular plants, show that the strange aspect 

 of the saprophytes and parasites devoid of chlorophyll is simply to be ascribed to the 

 want of chlorophyll; for the Loranthacese, with their little altered roots, absorb in 

 the main only water and mineral food-matters from the wood of the trees inhabited 



by them, and they are able, by means of their 

 shoots containing chlorophyll, to produce 

 organic substances by the decomposition of 

 the carbon dioxide of the atmosphere. In 

 accordance with this, the woody body of the 

 shoot-axis is strongly developed, the water 

 provided with mineral matters being con- 

 veyed through this to the assimilating leaves. 

 From the comparison of the Saprophytes 

 and Parasites with normal plants possessing 

 green leaves, we gain the conviction that the 

 whole vegetative segmentation, the distinction 

 of root and shoot, the differentiation of the 

 shoot into leaf and axis, and the production 

 of wood and other anatomical elements, have 

 essentially been called forth by the activity of the chlorophyll in nutrition. In pro- 

 portion as plants strive to present to the light and the air flat plates of tissue rich in 

 chlorophyll (i.e. leaves) from their shoot-axes, the shoot-axes must also develope 

 those forms of tissue which serve for the conveyance of nutritive materials 

 into the leaves and back from them; and, in proportion as this happens, the roots 

 contained in the substratum must also be capable of absorbing the water lost at the 

 evaporating leaves, together with the mineral matters necessary to assimilation. The 

 richer in chlorophyll and the larger the leaves (or the shoot-axes themselves, as in 

 the Cacti and cladodia), the more perfect also must the roots thus be. It is, 

 therefore, easily intelligible, that with increasing parasitism, — with the decrease, 

 and, finally, the entire disappearance of the chlorophyll-contents of the shoots, the 

 formation of roots also becomes simplified, and finally ceases altogether ; and that when 

 parasitism is carried to the highest degree, even the difierentiation of root, shoot, and 

 leaves in the vegetative body finally ceases, till, at last, the relation of plants of this 

 kind to highl}- organised phanerogams is recognised only in the development of the 

 flowers or inflorescences. Similar degradations are also met with in animal parasites. 



FIG. ^g.—Scybalütm fungifo 

 Kibes) the root of the host plant ; 

 niiinerous small flowers densely ci 

 face ; l< young shoot ; yy"fibro-vas 



(after Eichler). 



