226 Transactions British Mycological Society. 



colourless pseudoparenchymatous thin- walled cells which doubt- 

 less arose from a single hyphal cell amongst the dark fuscous 

 brown hyphae composing the stroma: these perithecial pri- 

 mordial cells stain deeply with iron-alum haematoxylin and are 

 larger in size and less delicate than the pseudoparenchyma 

 which initiates the formation of a pycnidial cavity. This pseudo- 

 parenchymatous mass of cells gradually increases in size and 

 though at first somewhat pear-shaped becomes more oval and 

 is elongated in the direction of the outer surface of the stroma 

 (fig. 7), where ultimately, at maturity, an ostiole with pro- 

 jecting hairs appears. At an early stage the cells in the centre 

 and lower part of this tissue begin to break down leaving multi- 

 nucleate protoplasts which tend to arrange themselves parallel 

 with the perithecial wall (figs. 7, 8). The cells forming the lining 

 of the basal part of the perithecium are now seen to be richly 

 protoplasmic and although multi-nucleate some of the nuclei 

 in them are larger than others and appear to be paired — such 

 cells giving rise to ascogenous hyphae (fig. 9, a, b). The asco- 

 genous hyphae are of the hooked type and in these could be seen 

 paired nuclei which had presumably arisen by conjugate division 

 of the paired nuclei of the basal cells from which they arise (fig. 9) ; 

 these hyphae much resembled those figured by Claussen(4) for 

 Pyronema confluens. 



Ascus formation from a penultimate cell could be seen 

 (fig. 9 a). Early stages of an ascus showed the usual paired nuclei 

 in the base of the ascus; later, the nuclei moved towards the 

 centre and in older asci the fusion nucleus occupied this position 

 (figs. 9fl and 7). As the asci develop they push aside the dis- 

 organising primordial pseudoparenchyma and occupy the space 

 and doubtless are nourished at the expense of the products of 

 the disorganised cells (fig. 7). At a still later stage the fusion 

 nucleus is replaced by eight smaller nuclei which become the , 

 centres of spore formation. Towards the periphery of the peri- 

 thecium many periphyses develop which bend upwards and 

 later outwards. By the presence of these protruding periphyses 

 developing perithecia could often be distinguished from de- 

 veloping pycnidia. 



The hfe history of this fungus shows points of similarity with 

 the life histories of other Ascomycetes. The conidial stage 

 prevails during summer and early autumn, and is followed in 

 later autumn by the pycnidial stage ; during winter the stromata 

 on the decaying leaves lying on the ground are set free and 

 behave as sclerotia, in which perithecial structures develop, and 

 thus by spring or early summer ascospores are mature and no 

 doubt are ejected from the asci on to young clover leaves, thus 

 causing the re-appearance of the disease. 



