37° 



LECTURE XXIII. 



An unusually simple and clear example of the penetration of the haustoria of 

 the parasite into the host-plant is found in the case of the mould fungus Pipiocephalis 

 Freseniana (Fig. 243). Both the parasite and the Mucor attacked by it are non- 

 cellular plants, consisting of simple tubular hyphae, various ramifications of which repre- 

 sent the organs. The figure shows the mycelial tubes m of the Piptocephalis 

 having become closely attached to the Mucor, M, and put forth root-like haustoria 



into the interior of the latter, by 

 means of which they absorb the 

 protoplasm of the Mucor and 

 transfer it to the parasite. 



In the form of haustoria the 

 parasite only penetrates the host- 

 plant by means of a small part of its 

 body. In the lectures on organo- 

 graphy, however, I have already 

 mentioned that under certain 

 circumstances the whole of the 

 vegetative body of a parasite may 

 be developed inside the host-plant. 

 In Fungi, e. g. the Peronosporeae, 

 jEcidiomycetes, etc., this is a very 

 common occurrence : only the 

 mature reproductive organs— and 

 even these not always — protrude 

 outside the tissues of the host- 

 plant. Similar cases also occur, 

 moreover, in Phanerogams which, 

 as follows from the structure of 

 their flowers, belong to highly- 

 organised types. According to the 

 remarkable investigations of Graf 

 zu Solms-Laubach, this is the case 

 especially in the RafBesiaceae, 

 where the whole of the vegeta- 

 tive body is developed in the 

 interior of the cortex and wood 

 of its host-plant. In these plants (Rafflesia, Brugmansia, Pilosiyles'^) parasitism 

 has had a degrading iniluence to so great an extent, that not only is the whole 

 vegetative body of the parasite enclosed in the tissues of the host-plant, and there 

 dispenses with any differentiation whatever into root and shoot, only consisting 

 in fact of growths of tissue between the tissues of the host-plant, but even the 

 flower-buds are formed in the interior of the host, only bursting through its cortex 

 and appearing in the open at the very last. In the case of Pilostyles, investigated 

 with particular care by Graf Solms-Laubach, and which dwells in the foliage shoots 



Fig. z^'^.—Piptoce^halis Fresentana (after Brefeld). M a portion 

 of the mycelium of Mucor Mucedo from which the mycelium ntjn-oi 

 the Piptocephalis obtains its nourishment; h haiistoria which have 

 penetrated the Mucor filaments; c conidiophore ; jj the two con- 

 jugating mycelial branches which form the zygospore Z. 



^ Graf ZU Solms-Laubach, Bot. Zeiig., 1874 (Nos. 4 and 5) and 1876 (p. 449). 



