186 REPRODUCTION 



F. Bachmann 1 was able to make important cytological observations in 

 her study of Collema pulposum. As regards the vegetative and ascogonial 

 nuclei, five or perhaps six chromosomes appeared on the spindle when the 

 nucleus divided. In the asci, the usual paired nuclei were present in the 

 early stages and did not fuse until the ascus had elongated considerably. 

 After fusion the definitive nucleus enlarged with the growth of the ascus 

 and did not divide until the ascus had attained full size. The nucleolus was 

 large, and usually excentric, and there were at first a number of chromatin 

 masses on an irregular spirem. In synapsis the spirem was drawn into a 

 compact mass, but after synapsis, "the chromatin is again in the form of 

 a knotty spirem." In late prophases the chromosomes, small ovoid bodies, 

 were scattered on the spindle; later they were aggregated in the centre, 

 and, in the early metaphase, about twelve were counted now split longi- 

 tudinally. There were thus twice as many chromosomes in the first division 

 in the ascus as in nuclear divisions of the vegetative hyphae. F. Bachmann 

 failed to see the second division; there were at least five chromosomes in the 

 third division. 



Considerable importance is given to the number of the chromosomes in 

 the successive divisions in the ascus since they are considered to be proof of 

 a previous double fusion in the ascogonium and again in the ascus necessi- 

 tating, therefore, a double reduction division to arrive at the gametophytic 

 or vegetative number of five or six chromosomes in the third division in the 

 ascus. There have been too few observations to draw any general conclusions. 



c. DEVELOPMENT OF SPORES. The spore wall begins to form, as in 

 Ascomycetes, at the apex of the nucleus with the curving over of the astral 

 threads, the nucleus at that stage presenting the figure of a flask the neck 

 of which is occupied by the centrosome. The final spore-nucleus, as observed 

 by Maire, divides once again in Anaptychia and division is followed by the 

 formation of a median septum, the mature spore being two-celled. In 

 Peltigera the spore is at first ovoid, but both nucleus and spore gradually elon- 

 gate. The fully formed spore is narrowly fusiform and by repeated nuclear 

 division and subsequent cross-septation it becomes 4- or even 5-6-celled. 



The spores of lichens are wholly fungoid, and, in many cases, form a 

 parallel series with the spores of the Ascomycetes. Markings of the epispore, 

 such as reticulations, spines, etc., are rarely present (Solortna spongiosa\ 

 though thickening of the wall occurs in many species (Pertusariae, etc.), a 

 peculiarity which was first pointed out by Mohl 2 who contrasted the spore 

 walls with the delicate membranes of other lichen cells. Some spores, 

 described as "halonate," have an outer gelatinous covering which probably 

 prevents the spore from drying up and thus prolongs the period of possible 

 germination. Both asci and spores are, as a rule, more sparingly produced 

 1 Bachmann 19x3. 2 Mohl 1833. 



