182 REPRODUCTION 



a. OPEN OR CLOSED APOTHECIA. Schwendener 1 drew attention to two 

 types of apothecia directly influenced by the thallus: those that are closed 

 at first and only open gradually, and those which are, as he says, open from 

 the first. The former occur in genera and species in which the thallus has a 

 stoutish cortex, as, for instance, in Lobaria where the young fructification 

 has all the appearance of an opening perithecium. The open apothecia 

 (primitus apertd) are found in non-corticate lichens, in which case the pioneer 

 paraphyses arrive at the surface easily and without any converging growth. 

 Similar apothecia are borne directly on the hypothallus at the periphery, or 

 between the thalline areolae, and they are also characteristic of thin or slender 

 thalli as in Coenogonium. 



In both types of apothecium, the paraphyses pierce the cortex (Fig. 100) 

 and secure the emergence of the. developing ascomata. 



Fig. too. Physcia ciliaris DC. Vertical section of apothe- 

 cium still coVered by the cortex, a, paraphyses; b, hypo- 

 thecium ; c, gonidia of thallus and amphithecium. x 150 

 (after Baur). 



b. EMERGENCE OF THE ASCOCARP. Hue" has taken up this subject in 

 recent years and has described the process by which the vegetative hyphae 

 surrounding the fruit primordium, excited to active growth by contact with 

 the generative system, take part in the later stages of fruit formation. The 

 primordium generally occupies a position near to, or just within, the upper 

 medulla, and the hyphae in contact with it soon begin to branch freely in a 

 vertical direction, surrounding the developing fruit and carrying it upwards 

 generally to a superficial position. The different methods of the final emer- 

 gence give two very distinct types of mature apothecium: the lecideine in 

 which the gonidial zone takes no part in the upward growth, and the leca- 

 norine into which the gonidia enter as an integral part. 



In the lecideine series (Fig. 101) the encircling hyphae from the upper 

 medulla rise as a compact column through the gonidial zone to the surface 

 of the thallus; they then spread radially before curving up to form the outer 

 1 Schwendener 1864. a Hue 1906. 



