228 RESEARCHES ON FUNGI 



(6) As long as primary conidia are growing in length, they remain 

 firmly attached to the top of the promycelium ; but, as soon as they 

 have attained full length and before conjugation has taken place, 

 they can be removed from the promycelium without difficulty. 

 Hanna has removed and sown large numbers of individual uncon- 

 jugated primary conidia ; many of these conidia have germinated, 

 and a few of them have developed a mycelium bearing secondary 

 conidia, as shown in Fig. 112. 



Brefeld x observed in Tilletia zonala that, if primary conidia, 

 before they have fused with one another, are pressed down beneath 

 the surface of the culture medium, they germinate individually and 

 that the germ -tubes or mycelia to which they give rise may develop 

 secondary conidia. He 2 also observed in T. controversa that any 

 unpaired primary conidium may germinate in a nutrient solution 

 and develop a mycelium bearing secondary conidia. 



Under natural conditions, doubtless, some primary conidia are 

 left unconjugated and it is possible that some of them succeed in 

 germinating. However, one may regard this mode of development 

 as abnormal and as but little likely to assist the fungus concerned in 

 propagating itself from one generation to another. 



External Conditions and the Germination of the Chlamydo- 

 spores. — As is well known, the chlamydospores of Tilletia tritici 

 will not germinate unless they are supplied with a sufficient amount 

 of moisture and are kept at a suitable temperature. According to 

 Woolman and Humphrey, 3 the minimum temperature for germina- 

 tion is 0°-l° C, the optimum 18°-20° C, and the maximum 

 20°-29-l°C. 



Some chlamydospores were placed upon agar in a Petri dish and 

 then a thin layer of sterile water was poured over them, so that 

 they were submerged. Some of the spores germinated, and their 

 promycelia grew upwards to the surface of the water. This experi- 

 ment affords conclusive evidence that chlamydospores are able to 

 germinate even although they are not in direct contact with the air. 



1 O. Brefeld, he. cit., Heft XII, 1895, p. 161, Plate X, Fig. 6. 



2 Ibid., p. 163. 



3 H. M. Woolman and H. B. Humphrey, Studies in the Physiology and Control 

 of Bunt or Stinking Smut of Wheat, U.S. Department of Agriculture, Bull. No. 1239, 

 1924, pp. 16-18. 



