28 Proceedings of the lioyul Irish Academy. 



stratification of which facilitates the splitting process. This power of the 

 hyphal tissue has been demonstrated by Lindau in his account of the develop- 

 ment of suckers. " The events which lead to the attachment of the thallus 

 are as follows : — Out of the superficial layer spring hyphae in thick bundles 

 of parallel threads which reach to the surface of the substratum, and here by 

 any crack leading into the loose tissue of the upper periderm layers act 

 exactly as the hyphae of the basal disc. . . ." 



Such a system, especially when composed of numerous haptera, is capable 

 of keeping pace with the development of the bark, and the thallus need not 

 be torn oil' by wind action when the outer periderm is quite dead. Probably 

 therefore the theories of Bornet 1 and Frank 3 are not mutually exclusive, 

 Bornet's theory being supported by the reproduction of Bamodmae by the 

 sucker and Btolon methods. Protococcm cells are very frequent on the 

 surfaces affected, and in two examples, one of B. Farlnacca and one of 



Xamih ' parieiina, were found in the periderm some distance below the 



surface, apparently unconnected with any hyphae or hyphal mass. No clear 

 case has yet, however, arisen to prove conclusively that a young plant is 

 directly or Bolely connected with the parent plant by means of an intraperi 

 dermal hyphal strand. In must oases the evidence consists of the existence of 

 such Btranda running mure or less horizontally along the twig, a state of 

 affairs comparable with the " Flechtenmycel " of Zukal, which he defines 



Fiiufsliick, p. 8) as " hyphal coiuple\ usually arising from an old lichen 



thallus, which often permeates the substratum for a foot's length, and gives 



at single points to new thallus formations, e.g., in 1'e/lidca venosa, 



S rrina sa L ■- Bcrtcposus, XarUhoria parieiina, Clculonia 



■ . >vc." 



The surface of a twig is frequently covered by a more or less continuous 

 gonidial layer which is too uniform to lie considered as soredial in character, 

 though possibly fragments rounded "I) in times <>( drought may act as soredia, 

 or under other adverse circumstances may produce the familiar Lepraria 

 forms. There is, as yet, no evidence, in the case of Ramalinu, of direct 

 vertical connection between this superficial layer and the intraperidermal 

 hyphal strands, except where a plant-outgrowth occurs. The conjunction 

 of these strands, at a favourable crack or lenticel, may be the determining 

 condition for the development of a new plant. Again, Xanthoria supplies 

 suggestive evidence. A specimen growing on a twig of Hawthorn with 



B rue:, K. Recherche* sur les goiiidies ties Lichens. Ann. des Sc. Nat., oser. Bot. 

 1873, xvii, p. 45. 



'Frank, A. B. " Obex diu biologiaohen Verhiltnisse dus Thallus emger Krusten- 

 lletchtcu Cohn's Ucker," 1S77, li, p. 133. 



