Sti)iking Smut or Bunt in Wheat. 71 



in the air and not in fluid. If germination takes place in damp air then 

 the promyceUum is short, but if in a dense layer of water then it is long. 

 The contents of the spore pass into the tube, and then the contents of the tube 

 collect in the growing apex, and if this grows further the tube becomes divided 

 regularly by transverse septa. Lateral branches may also be formed which 

 grow in a similar fashion. 



The mature conidia are filiform bodies arising from fine tubercles at the 

 apex of the promycelium, curved in various ways and varying in number 

 from four to twelve or more. They usually become united in pairs by the 

 outgrowth of a narrow tube passing from, the one and fusing with the other, 

 giving the appearance of the letter H. After this fusion germination occurs 

 by the production of a slender filament bearing a sickle-shaped secondary 

 conidium at its apex, into which the contents of the united spores have 

 migrated. According to Kuehn^ both the primary and secondary conidia 

 when placed in a damp atmosphere can give rise to a germ-tube which is 

 capable of infecting the wheat plant. 



The primary conidia may become detached before germinating, and then 

 fusion between them is not so likely, but when it occurs the connecting 

 bridge is wider. Brefeld found that the conidia which did not fuse behaved 

 similarly to those which paired, only the resulting germ-tubes and conidia 

 were smaller and shorter. Three or more primary conidia have been 

 seen connected, and double fusion between two has occasionally been 

 observed. 



Thus the normal mode of germination is for the spore to produce a stout 

 promycelium bearing a tuft of primary conidia at its apex, and each of these 

 conidia or the conidia miited Ln pairs to produce a single secondary conidium, 

 which puts forth a slender germ-tube to infect the wheat plant. 



We must carefully distinguish, however, between w^hat takes place in 

 water or in moist air and in a nutrient solution. While the spores germinate 

 freely in water, they do not succeed in a nutrient solution, Brefeld there- 

 fore first germinated the spores in water up to the formation of primary and 

 secondary conidia, and then added a nutrient solution. Both primary and 

 secondary conidia produce germ-tubes which develop into a much-branched 

 mycelium, just like a tuft of mould, the hyphae of which are exceedingly fine. 

 On the aerial branches numerous short lateral shoots are formed which swell 

 up at their ends and become crescent-shaped conidia (Fig. M). These are 

 easily detached, and again give rise to a tufted mycelium capable of producing 

 further conidia in the manner already described, and this continues as long 

 as the culture is maintained in the nutrient solution. Xo conjugations or 

 fusions occur among these conidia. The branches of the mycelium which are 

 given off in the nutrient fluid do not produce conidia, but grow outwards 

 until they reach the air, when they produce terminal conidia or remain 

 sterile, in which case the liyphaj are septate and appear empty. 



Adaptations to Unfavorable Conditions. 



This account of germination would not be complete without referring to 

 the curious adaptations which Brefeld has observed to occur during germi- 

 nation, in order to provide against or to escape unfavorable conditions. 



1. If the spores are submerged or the detached conidia fall into water, 

 they only produce a germ-tube which must either enter the wheat-plant or 

 die. The spores do not produce pi'imary conidia, nor the primary conidia 

 secondary conidia, because it would be a useless waste of energy, as they would 

 be sure to perish in the superabundant moisture. 



