26'8 EEV. J. M. CBOMBIE ON THE ALGO-LICnEN HYPOTHESIS. 



according to the principle involved in their theory and upon 

 which it is directly founded *. This is fully corroborated by the 

 observations of Mr. Marshall Ward on Strigula complanata, Tee 

 (vide Trans. Linn. Soc, Bot, vol. ii. pt. 6, 1884), though the 

 author strangely fancies these to be entirely confirmatory of the 

 Algo-lichen hypothesis. The fungal-mycelium of which he speaks 

 as occurring so frequently on the leaf of Michelia, &c, and comiug 

 into contact with the assumed algals, that is the "platygonidia " 

 of Strigula (in which even when fertile there are scarcely any or 

 no licheno-hyph® present), at length, as he acknowledges, destroys 

 the " algals," which it invests with its meshes. The same phe- 

 nomenon also takes place in our British species of Strigula, viz. 

 S. Babingtonii, when similarly invaded by the proto-hypluB of Cap- 

 nodium Footii, with which it is often associated on the same leaf. 

 But apart altogether from such considerations relating to 

 lichen- culture, there are two fatal objections to the hypothesis, 

 either of which is quite sufficient for its subversion. The first 

 of these has reference to the very peculiar nature of the parasitism 

 involved in the theory that the fungal-hyphao are nourished by 

 the captive algals. Other plants, from which parasites draw 

 their nourishment, usually become speedily exhausted and finally 

 perish, often involving in their death that of the parasite itself. 

 In some cases, indeed, where the host is of sufficient size and 

 vigour to supply food alike for its guest and itself, it may, for a 

 more or less protracted period, suifer but little injury. But here 

 we have a parasite exceeding in size and number of cells by many 

 hundred times the nourishing plant which it invests, and yet, so 

 far from exhausting, only invigorating its host — a phenomenon 

 which certainly nowhere else occurs in nature (vide Caspary, 

 " TJeber die neueren Ansichten in Betreff der Mcchten," &c, 

 1872). Such parasitism is indeed acknowledged by Schwendener 

 himself, in the last of the memoirs above cited, as being unique 

 in the Vegetable Kingdom. At the same time he fancied that the 

 AWoc-chaplets recorded by Strasburger as occurring in the leaves 

 of Azorella, by Keinke on the stems of some species of Gunnera, 

 by Janczewski in the interior of Anthoceros, and by Cohn in the 

 tissues of Lemna, have brought to notice cases of adaptation in a 



* Strange to say, however, according to the observations of M. Bonnier (vide 

 Bull. Soc. Bot. Fr. 1883, p. 87) a lichen does not require any algal whatever for 

 its fabrication. This new discoverer has himself made lichens from the proto- 

 plasm of " Mosses" associated with spores, — a new kind of Commensalism of 

 which even Schwendener never dreamed. 



