i;2 



REPRODUCTION 



blue with iodine, mount upwards from that region through the medulla and 

 gonidial zone 1 . The ascogonium does not appear till the surface is almost 

 reached. 



cc. GRAPHIDEAE. Several members of the Graphidaceae were studied 

 by G. Wolff 2 : she demonstrated the presence of carpogonia with emerging 

 trichogynes in Graphis elegans, a species which is distinguished by the deeply 

 furrowed margins of the lirellae (Fig. 89). Before the carpogonia appeared 

 it was possible to distinguish the cushion-like primordial tissue of the apo- 

 thecium in the thallus which is almost wholly immersed in the periderm 

 layers of the bark on which it grows. The trichogynes were very sparingly 

 septate, and a rather large nucleus occupied a position near the tip of the 

 terminal cell. The dark carbonaceous outer wall makes its appearance in 

 this species at an early stage of development along the sides of the lirellae, 

 but never below, as there is always a layer of living cells at the base. After 

 the first-formed hymenium is exhausted, these basal cells develop a new 

 apothecium with a new carbonaceous wall that pushes back the first-formed, 

 leaving a cleft between the old and the new. This regenerating process, 

 somewhat analogous to the formation of new apothecia in Pertusaria, may 

 be repeated in Graphis elegans as many as five times, the traces of the older 

 discs being clearly seen in the channelled margins of the lirellae. 



dd. CLADONIAE. The chief points of interest in the Cladoniae are the 

 position of the apothecial primordia and the function of the podetium, 



\rhich are discussed later 8 . Krabbe 4 deter- 

 mined not only the endogenous origin of 

 the podetium but also the appearance of 

 fertile cells in the primordium (Fig. 98). 

 Both frequently take rise where a crack 

 occurs in the cortex of the primary squa- 

 mule, the cells of the gonidial tissue being 

 especially active at these somewhat ex- 



P SCd P 1 * 065 ' The fertile ^P 1 6 elongate 



and branch within the stalk of the de- 



i j . . < 



veloping podetium, sometimes very early, 

 O r not until there is a pause in growth, 

 when carpogonia are formed. As a rule 

 trichogynes emerge in great numbers 2 , generally close to, or rather below, 

 the spermogonia. In Cl. pyxidata* the carpogonia are characterized by the 

 large diameter of the cells three to five times that of the vegetative hyphae. 

 Though most of the trichogynes disappear at an early stage, some of them 

 may persist for a considerable period. As development proceeds, the vege- 

 tative hyphae interspersed among the ascogonial cells grow upwards, slender 



1 See also p. 147. Wolff 1905. 3 See Chap. VII. 4 Krabbe 1883 and 1891. 6 Baur 1904. 



Fig. 98. Cladonia deeorticata Spreng. Ver- 



tical section of squamule and primordium 



of podetium. a, developing podetium; 



6, probably fertile hypfiae; c, cortical 

 tissue ; </, gonidial cells, j x 600 (after 



