28 



R.OBER I S. KlKBY 



'The germ tube, after its first appearance, grows rapidly and may reach a 

 length of 55 /j. and 300 /x in 24 and 48 hours, respectively. The germ 

 tube is hyaline. Septa are not developed until during the second day's 

 growth. Guttulae or fat globules are found in the germ tubes after the 

 septa are laid down. These observations agree with those of Delacroix 

 (1901), McAlpine (1904), and Hori (1901), except that Hori appears 

 never to have observed germ tubes arising from the middle of the ascospore. 



The effect of varying degrees of acidity on ascospore germination was 

 determined by germinating aseospores in thirteen different solutions pre- 

 pared with hydrochloric acid and sodium hydroxide and ranging in acidity 

 from pH 3 to 10. The results of this test are shown in figure 2. 

 The bimodal germination curve shows that aseospores of this fungus 



Per cent of 

 germination 



4 5 6 7 8 9 10 



pH of solution 



Figure 2. percentage of ascospores of ophiobolus cariceti germinating at 

 varying degrees of acidity 



germinate through a smaller range of acidity than that in which growth 

 takes place. The rate of growth of the germ tubes in the solutions of 

 different pH values was greatest at pH 7 and was only slightly less at 

 pH 8 (hyphae 180 n long in 48 hours . 



Concerning penetration, Mangin (1899) reports that the germ tube 

 creeps along the surface of the root hairs and soon pierces the membrane 

 and enters the interior of the plant. In the present investigations, wheat 

 plants growing in pure culture in test tubes on 0.2-per-cent dextrose and 

 potato agars in petri dishes were inoculated with ascospores, and the 

 growth and penetration of the germ tube were observed under the micro- 

 scope. Approximately fifty inoculations were made in this manner, and 

 it was noted that the germ tube of the pathogene grew along the surface 

 of the roots and nearly always entered the epidermis directly. In one 

 case a hypha formed a small appressorium on a root hair, and from this 



