24 GENERAL MORPHOLOGY. 



In some instances this articulation and formation of ger- 

 minative cells goes a step farther in order to ensure the attain- 

 ment of its purpose, inasmuch as the cells are formed into 

 veritable resting cells, whereas, as a rule, the oidia cannot be 

 characterised as such, their powers of resistance being no greater 

 than those of the mycelium from which they are elaborated. 

 The conversion into resting cells may be effected by the 

 thickening of the membrane of the oidia, and the absorption of 

 nutrient material fiom the adjacent portions of the mycelial 

 plasma, in consequence of which the cell in question increases 

 in size. Owing to the large fat content of these cells, they 

 strongly refract light, and thus show up with particular lustre 



Fig. 105. — Chlamydomucor racemosus Brefeld. 



Fragment of mycelium which has undergone conversiou into chains of oidia. ilagn. 

 120. iA/ter Brefeld.) 



(like a cut precious stone (gemma) in a necklace) against the 

 exhausted adjoining portions of the hypha. Such a cell is 

 termed a gemma, chlamydospore, or brood cell. They are 

 more usually formed in the mycelial hj-phae, but occasionally 

 also appear on fruit-bearing stems, which have either fulfilled 

 their true purpose or are in the act of so doing. An example of 

 both instances is shown in Fig. 106. In each case the gemmae 

 have been produced within the hypha, or conidium, and are 

 therefore intercalary ; though instances are known where the 

 gemma is formed on the crown of an erect hypha, on which it is 

 .supported as by a stem, and is therefore known as a peduncular 

 gemma. The fir,st observation of the production of chlamydo- 

 spores was made in 1S85 by Caspary (I.), who recognised them 

 as a new method of fructification and gave them the name 

 arthrospores, which, however, is no longer used in this sense 



(§55)-. 



With regard to the arbitrary production or suppression of 

 gemmjB, certain experiments were made on Mortierella van 

 Tie(ihf;riui by J. Bachmann (II.), who found that, in cultures on a 

 solid nutrient substratum, concentration of the medium restricts 



