422 



BOTANICAL GAZETTE [may 



rapidity of growth, and it is assumed that for this reason increase or decrease of 

 moisture in the surrounding air does not affect the proportion between zygospores 

 and sporangia. Upon certain substrata, zygospores are more abundant at the 

 junction of adjacent mycelial colonies, forming dark lines. The conditions 

 governing their production have not been investigated. 



For several years Dauphin has been interested in the genus Mortierella. In 

 a recent paper on the genus 1 3 he gives in 28 pages a systematic arrangement of the 

 species as an introduction to a special study of M. polycephala. The original 

 descriptions and figures are given for each of the 29 species and varieties dis- 

 cussed. Two new species, M. canina and M. raphani, and one new variety, M. 

 van Tieghemi var. cannabis, are described. The genus is divided into four group 

 species (grandes especes) with subspecies (petites especes) and varieties under 

 them. A well-arranged key would have added to the value of this part of the work. 

 M. polycephala is the only one of the Mortierellas which has been investigated in 

 regard to the influence of external conditions upon the production of zygospores. 

 In this species, which forms the subject of the physiological part of the paper, 

 Dauphin has succeeded in finding the zygospores, and since he obtains them from 

 sowings of single spores, he classifies the species as homothallic. This being t e 

 case, it seems strange that they have not been found in this form by other investi- 

 gators, since as yet no neutral strains have been found for homothallic species^ 

 The optimum temperature for germination of the spores is placed at 27 L -> *" 

 the optimum for formation of sporangia and zygospores, between 15 and 20 

 Germination and growth are checked by darkness, but the fructifications are not 

 altered. Light increases the rapidity of development, but if too intense causes 

 the fructification to be confined to stylospores. The violet and ultra-violet rays 

 the spectrum seem necessary for the germination of the spores. X-rays an 

 influence of radium are inhibitive to germination and growth, the radium in addition 

 causing the production of cysts in the hyphae. Moisture in the surrounding air is 



germination 



Perfect 



A 

 development will take place in an atmosphere completely free from oxygen. 



decrease, however, of atmospheric pressure below iSo mm causes the mycelium J> 

 remain sterile. An increase of pressure above atmospheric checks the grow 

 the mycelium without preventing the normal fructifications. M. P° y c P [ 

 like other mucors, develops poorly in liquid media. The monosacchands, #P^ 

 cially dextrose and levulose, were found most favorable of the carbohy ra 



The influence of different concentrations 



formation 



of the nutrient was little investigated, but stylospores and sporangia ^ ^ 

 duced without zygospores when the amount of dextrose was increase ro ^ 

 per cent, to 60 per cent. The purpose of this part of the paper seems to a\ e ^ 

 to find out the influence of a large number of more or less isolated extern * hc 



ditions upon the form of fructification, 

 influence of a few closelv related factors. 



" " c •; Nat. Bot- 



«3 Dauphin-, Jean, Contribution a I'etude des Mortierellees. Ann. be . 



IX. 8: 1-112. 1908. 



