INFLUENCE OF EXTERNAL STIMULI. THE MEDIUM 267 



circumstances on the mycelium of Mucor racemosus 1 , behave in quite the 

 same way ; the formation of sporangia takes place here only in the air, 

 in a fluid the gemmae form mycelia. If Mucor racemosus grows in a 

 nourishing solution of some depth rich in sugar, its mycelium forms septa 

 and a series of cells rich in plasm is developed. If the depth of the 

 solution be shallow, and the solution itself dilute, phenomena like those 

 which are the result of bad nutrition appear the protoplasm of the 

 mycelium aggregates and becomes so divided by septa that a series of 



Jl 



FIG. 1.29. Mucor Mucedo. Stages in the forma- 

 tion and germination of the zygospore. i, myce- 



lial branches conjugating. 2, abjunction of the . 



conjugating cells a a from the suspensors b b. I'IG. MO. Ampelopsis. len- 



>,. conjugating cells more evident, warts on the ils, R with anchoring disks at 



membrane, beginning to form. 4, ripe zygospore the ends of the branches. Lelirb. 



b between the suspensors a. 5, sporophore arising 

 directly from the zygospore. After Brefeld. 1-4 

 inagn. 225; 5 magn. about 60. Lehrb. 



chambers alternately rich in protoplasm and empty of protoplasm are 

 produced a process recalling the formation of isolated cells by the 

 protonema of many mosses 2 . 



The mycelium of Mucor racemosus, but not that of Mucor Mucedo, 

 can on the other hand pass over into the sprouting form. This happens if 



1 Brefeld, Untersuchungen ans clem Gesammtgebiete cler Mykologie, viii. p. 212; Klebs, Die 

 Bedingungen der Fortpflanzung bei einigen Algen und Pilzen, p. 496. To the latter work I refer for 

 an exhaustive account of the conditions determining the appearance of mycelium and sporophore. 



2 See p. 262. 



