.NOURISHMENT OF PARASITES. 369 



extent as vascular bundles for the parasite. Still more striking is the morphological 

 change suffered by the branches of Pine-trees infested by the fungus jEct'dium 

 Elatinum; these are known under the name of Witches Brooms, and are distin- 

 guished by a form of branching otherwise foreign to the lateral shoots of the Pine, 

 and their needle-like leaves fall off like those of summer plants, to be renewed 

 annually. Such a branch of the Pine attacked by the Fungus exists on the 

 mother-branch in the form of a small deciduous Fir-tree, which may become 

 ten years or more old (De Bary^). Euphorbia cyparissias, so very common in 

 Germany, also has its whole habit altered by a Fungus {^cidium) dwelling in its 

 tissues. 



No less remarkable is the chemical influence of many Fungi on their nutritive 

 substratum, in so far that they not only extract from it the material necessary for 

 their nourishment, but, in addition, cause the destruction of organic substances 

 quite unnecessarily, so to speak, and even to their own injury. The Fungus 

 (Phytophthora in/estans) which causes the potato disease, for instance, vegetates 

 in the tissues of the Potato-shoot, in the first place in order to nourish itself: 

 when its fructification protrudes through the stomata of the shoot, however, a 

 decomposition of the organic matters in the tissues of the latter is set up, which kills 

 the Potato-shoot itself, and makes the further nutrition of the parasite impossible. 

 In the same way, by the mycelium of Mucor Mtuedo developing in a fresh Apple, the 

 tissue of the fruit is not merely extracted for the nourishment of the Fungus, but is 

 at the same time converted into a soft smeary mass, alcohol and ethereal oils being 

 formed. The most striking of such cases are the decompositions of the media 

 not directly serving for nutrition, by the ferment fungi (Yeast) and Bacteria; 

 while these Fungi take up from their substratum only exceeding small quantities 

 of sugar and proteids for their own nourishment, they destroy enormous quantities of 

 these substances by profound decompositions. Many fungi which kill trees by 

 destroying the wood behave similarly. 



Regarding still further the ways and means by which these plants are 

 connected with their substratum, we find conspicuous differences even in the case of 

 parasites. In the first place, the parasite may, on the whole, exist and grow entirely 

 external to the host-plant, only being placed in connection with its tissues by means of 

 peculiar, relatively small organs, the so-called haustoria, as is to be seen particularly 

 clearly in the Cuscutese and in Thesium and Rhinanthus : these haustoria are, as has 

 already been shown in the organographical introduction, metamorphosed roots 

 which penetrate into the tissues of the host-plant. According to circumstances, this 

 metamorphosis is only inconsiderable, as in the Miselto, which abounds in chloro- 

 phyll, and the whole root-system of which is contained in the host-plant ; or the roots 

 are converted into haustoria and lose their typical character entirely, as has already 

 been described in the case of Cuscuta, where the tissue of the haustorium breaks up 

 within the host-plant into single filaments of cells. In saprophytes also, especially 

 the Orchideae containing little or no chlorophyll, a degradation of the root-system 

 makes itself evident, in that the roots remain shore, are very thick, branch but little, 

 and form either no root-cap at all or but a very feeble one. 



' De Bary, 'Die Erscheinung der Symbiose! p. 27 (.Strasbnrg, 1879). 

 [3] B b 



