REPRODUCTION IN DISCOLICHENS 



173 



branches push up between them and gradually a compact sheath of para- 

 physes is built up. The ascogenous hyphae meanwhile spread radially at 

 the base of the paraphyses and the asci begin to form. The apothecia may 

 be further enlarged by intercalary growth, and this vigorous development 

 of vegetative tissue immediately underneath raises the whole fruit structure 

 well above the surface level. 



Sattler^ in his paper on Cladoniae'^ cites as an argument in favour of 

 fertilization the relative positions of carpogonia and spermogonia on the 

 podetia. The carpogonia with their emerging trichogynes being situated 

 rather below the spermogonia. Both organs, he states, have been demon- 

 strated in eleven species; he himself observed them in the primordial podetia 

 of Cladonia botrytes and of CI. Floerkeana. 



2. PYRENOLICHENS 



a. Development of the Perithecium. It is to Fuisting" that we 

 owe the first account of development in the lichen perithecium. Though 

 he failed to see the earlier stages (in Verrucaria Dufourii), he recognized 

 the primordial complex of hyphae in the gonidial zone of the thallus, from 

 which originated a vertical strand of hyphae destined to form the tubular 

 neck of the perithecium. Growth in the lower part is in abeyance for 

 a time, and it is only after the neck is formed, and the fruiting body is 

 widened by the ingrowth of external hyphae, that the asci begin to branch 

 up from the tissue at the base. 



b. Formation of Carpogonia. Stahl* had indicated that not only 

 in gymnocarpous but also in angiocarpous 

 lichens, it would be found that carpo- 

 gonia were formed as in Collema. Baur° 

 justified this surmise, and demonstrated the 

 presence of ascogonia in groups of three to 

 eight, with trichogynes that reached the 

 surface in Endocarpott {Dermatocarpon) mi- 

 niatmn (Fig. 99). It is one of the few 

 fohaceous Fyrenolichens, and the leathery 

 thallus is attached to the substratum by a 

 central point, thus allowing in the thallus 

 not only peripheral but also intercalary 

 growth, the latter specially active round the 

 point of basal attachment; carpogonia may 

 be found in any region where the tissue is 

 newly formed, and at any season. The upper 

 cortex is composed of short-celled thick- 



' Sattler 1914. = gee Chap. VII. " Fuisting 1868. « Stahl 1877. ^ g^ur 1904. 



Fig. 99. Dermatocarpon miniatum 

 Th. Fr. Vertical section of thallus 

 and carpogonial group x 600 (after 

 Baur). 



