TILLETIA TRITICI 221 



two primary conidia, the nucleus present in one of the conidia 

 passes via the bridging hypha into the other conidium, so that this 

 becomes binucleate. Thus two nuclei of opposite sex become 

 associated with one another. The long slender curving form of 

 the primary conidia must favour the chance of two conidia of 

 opposite sex coming sufficiently near one another to make conjugation 

 possible. 



Variations in the Development of the Primary and Secondary 

 Conidia. — After conjugation has been completed, further develop- 

 ment of the H -shaped pairs of primary conidia may take place in 

 any one of five ways. These will now be considered seriatim. 



(1) The pairs of primary conidia remain seated on the promy- 

 celium, and each pair puts out laterally a short pointed hypha or 

 sterigma (st in Fig. 107, F) upon which there develops a single 

 secondary conidium (s) which is soon violently discharged. In 

 Fig. 108 is shown the whole of a basidium with six pairs of primary 

 conidia producing and discharging secondary conidia. Whilst each 

 pair of primary conidia is producing a secondary conidium, the 

 protoplasm of the pair of primary conidia passes en masse into the 

 secondary conidium (Fig. 107, F) ; and, after a secondary conidium 

 has been shot away, the H -shaped pair of primary conidia which 

 produced it is a dead structure, devoid of protoplasm, and quite 

 incapable of developing any further. The mode of development 

 just described and represented in Figs. 107, F, and 108, must be 

 considered as fully normal. It takes place regularly when chlamy- 

 dospores are sown on a solid medium such as dung-agar, under 

 suitable conditions of temperature and ventilation, and are not 

 mechanically disturbed ; and no doubt it takes place under natural 

 conditions. 



When one looks down on a chlamydospore culture with the low 

 power of the microscope, one can often observe tufts of primary 

 conidia which bear two secondary conidia (Fig. 107, F) and, occa- 

 sionally, a tuft which bears as many as three or four secondary 

 conidia (Fig. 108). In any tuft, the H -shaped pairs of primary 

 conidia develop and discharge their secondary conidia not of 

 necessity simultaneously, but often in succession. Hence the full 

 number of secondary conidia produced by a tuft of primary conidia 



