8 Brierley, Life-Htstory of LgptosphcBria Lcmmiece. 



These branch freely and very irregularly in the perithecial 

 tissues, and the nuclei pass into them in pairs. (P/. /., 

 Figs. 13, 14.) 



Walls are laid down, and from apparently any of the 

 binucleate cells thus formed asci may arise.* {PL /., 

 Figs. 13, 14.) 



The binucleate stage of the nscus lasts for a short 

 time only, the nuclei rapidlv- fusing^. 



During this development of the asci the enveloping 

 hyplue have continued to grow, and the necessary space 

 is gained by the pressure apart and degeneration of the 

 host cells in contact with the ascocarp. There is usually 

 early differentiation of the surrounding tissues, the wall 

 layer becoming apparent as consisting of somewhat 

 elongated and flattened polyhedral-shaped peripheral cells, 

 from which intercellular hyphre and haustoria arise. 

 These cells are especially active in growth, and remain 

 thin-walled until the perithecium is nearly mature. 

 Immediately internal are a few layers of firm, thin-walled 

 tissue, whilst centrally, amidst which the ascogenous 

 elements lie, are very delicate cells. The components of 

 this sterile perithecial tissue are somewhat flattened and 

 polygonal in shape and constantly uninucleate. They do 

 not hold stain, and stand in contrast to the more deeply 

 stained multinucleate ascogenous elements {PL /., Fig. 

 \2\{Pl. II., Fig 16.) 



The asci develop rapidly and soon appear as swollen 

 oblong sac-like bodies, flattened by pressure in their 



For a discussion of the interest of such paired nuclei see — 

 J. H. Faull, "Cytology of Laboulbeiiia chu'top/io7-a am\ /.. i^yriindantm'' 

 Anns. Bot. , XXVI. 1 9 1 2. 

 * For a different interpretation of this and the similar cases described 

 by Faull ("Development of llie Ascus and Spore I'ormation in Ascomy- 

 ceies," Proc. Bos/on .Soc. Nat. Hist., 32, 1905), see Brown (" The 

 Development of the Ascocarp ai Lfottia." Bot. Gaz., 50, 1910). 



