i6 



GENERAL MORPHOLOGY. 



Eumycetes 



(Acrogenous- 



fungi). 



Mycomycetes 



(with septate 



mycelium). 



Phycomycetes 



(aseptate 



mycelium). 



without endogenous spores-! 

 ivith endogenous spores . 



without oogonia . . . . ] 

 without zoosporangia, but 



producing zygospores .J 

 with oogonia and zoospor- 1 



angia j 



with zoosporangia . . . 



Class. 

 All other 

 Mycomycetes. 

 Ascomycetes. 



Zygomycetes. 



Oomycetes 

 ChytridiacecE. 



The cause of the upward growth of the aerial hyphse — both 

 those bearing sporangia, and those putting forth the conidia to 

 be described later on — has already been the subject of repeated 

 investigation. What is it that causes these hyphse to raise 

 themselves from the mycelium and extend vertically upwards ? 

 In accordance with its destiny, the aerial hypha draws on the 

 rich store of material in the mycelium, for the purpose of 

 producing spores and filling them with an accumulation of 

 matter. This material, being taken up in the dissolved state, 

 needs to be freed from solvents in order to secure its deposition ; 

 and the process can only be cariied out on a large scale in an 

 environment comparatively poor in moisture, a condition that is 

 only fulfilled ahore, but not ivifliin, the aqueous or damp nutrient 

 medium. Consequently the fruit-bearing aerial hyphse grow 

 upwards into the air. This turning away from water is termed 

 negative hydrotropism, and was first recognised, by J. Wortmann 

 (XIV.) in 1 88 1, in the aerial hyphse of Ph ycojnijces nitens. 

 Communications on the same point having also been published 

 by L. EuRERA (IX.), the above-mentioned state of things was 

 afterwards recognised by G. Klebs (I.) on the basis of his 

 researches on the conidiferous hyphae of Aspergillus {Eurotium) 

 repens and the sporangiferous hyphaj of Sporodinid grandis. That 

 other functions, such as heliotropism (see § 233), may be mani- 

 fested concurrently with negative hydrotropism is a matter of 

 course. In connection with the dependence of sporangiation 

 upon the conditions of nutrition, thoroughgoing investigations 

 were conducted by Klebs (I.) on Rhizopus {Mucor) stolonifer ; and 

 this worker ascertained the definitive factor to be the percentage 

 of moisture in the superincumbent atmosphere. J. Bachmann 

 (II.) then showed that Mortierella van Tieghemii (see § 237) 

 produces spores only when sown on a solid (not liquid) nutrient 

 substratum, and then only provided the temperatvu-e does not 

 fall below 20° C. 



§ 221.— Fructification by Zyg-ospores. 



Zygospores are the result of the encounter of two hyphse, or 

 the fusion of two cells, and are produced in the following manner 

 (Fig. 10 1). Two of the mycelial hyphte coalesce, the crowns 



