HYPOCREALES 



249 



protoplasm, divide much and grow to a column of tissue (Fig. 162, E) 

 which ruptures the rind and develops the usual perithecial heads (Vin- 

 cens, 1917; Killian, 1919). Sexual organs are formed in them in regular 

 positions in the peripheral layer (Fig. 163) and are little differentiated 

 from the surrounding vegetative tissues. Their first fundament consists 

 of a multinucleate, elongate hypha, rich in protoplasm and arising from 





Fig. 163. — Clariceps -purpurea. Diagrammatic section through a head showing primordia 



of perithecia. (After Killian, 1919.) 



an empty vegetative cell (Fig. 164, 1). It is usually unbranched. The 

 terminal cell swells, the nuclei divide and arrange themselves in pairs. 

 They form two or three unicellular branches which bend toward each 

 other and lie over one another (Fig. 164, 2). These branches take up the 

 dicaryons, elongate considerably, and undergo repeated nuclear division; 

 thereby the central branch, the future ascogonium, remains shorter 

 and thicker; while the other branch (or both other branches), the future 

 antheridium, is longer and more slender (Fig. 164, 3). The ascogonium 



