122 



FIRST GROUP. THALLOPHYTES. 



The trichogyne also suffers characteristic changes in consequence of fertilisation. 

 While the cells of the ascogone increase in size, those of the trichogyne lose a portion 

 of their original volume ; the transverse septa swell up into thick strongly refractive 

 nodes, so that the trichogyne which was before of uniform thickness assumes a 

 nodose appearance ; the protoplasmic contents of its cells also become brown. The 

 phenomena of reproduction are quite similar in other Collemaceae. Physma com- 

 pactum is peculiar in one respect ; the apothecia are formed in the tissue which con- 

 stitutes the envelope of the spermogonia. From the base of this receptacle hyphal 

 filaments grow up and form procarps. This species may therefore be said to be 



FIG. 81. Anaptychia ciliaris, a small portion of the apothecium in vertical section; m medullary layer 

 of the thallus, y the subhymenial layer,/ paraphyses of the hymenium ; between them are the asci in different 

 stages of development ; in i the young spores are not yet septate, in 2 4 the spores are more advanced ; the 

 protoplasm in which they are imbedded is contracted by the drying up of the Lichen before the preparation 

 was made. Magn. 350 times. 



hermaphrodite, since spermatia and carpogone are derived from common hyphal 

 layers. The envelope of the apothecium in this case is not as in Collcma a result of 

 fertilisation, but was in existence before as the envelope of the spermogonia. 



The club-shaped spore-sacs (asci) of the Lichens resemble those of the Pyrenomy- 

 cetes and Discomycetes in every important point ; their wall is often very thick and 

 has great power of swelling ; the spores too (Fig. 82), as in the Fungi just mentioned, 

 are the result of a process of free cell-formation, in which a portion of the protoplasm, 

 and often a considerable portion, remains unused. The normal number of the spores 

 is eight, sometimes only one to two, as in Umbilicaria and Mcgalospora, from two to 

 three or four to six in some species of Pertusaria ; some hundreds even are found in one 



