56 STIMULATIVE INFLUENCES. 



being heightened by the determinations of Oltmanns. Accord- 

 ing to H. Hoffmann (II.), E. Loew (III.)) ^^^ A.. Lendner (I.), 

 the formation of sporangia or conidia in Rliizopus nvjricans, 

 lliamnidium eler/ans, and Mucor vnicedo, or PpniciUium gJaucum 

 and Trichuthecmm ro^eum respectively, proceeds just as well by 

 daylight as in the dark. C. Werner (I.) also failed to detect 

 any influence of light on the formation of conidia in two of the 

 higher Ascomycetes. In the case of Botrytis ciiierea — according 

 to RiNDFLEisCH (I.) — this formation occurs solely by night ; and 

 in this instance, as was determined by L. Klein (III.), the 

 retardation is attributable mainly to the blue-violet rays of the 

 spectrum. The converse has been observed in the case of 

 Rhizopus nigricans, which, according to A. Lendner, puts forth 

 its sporangia two days later in the dark, or in red and yellow 

 light, than in white, blue, or violet light. In the dark, Mucor 

 raremosus produces merely barren sporangia ; whilst, in the case 

 of the Thamnidium aurantiacuvi described by Rochard (I.), this 

 fructification is said to proceed most favourably in twilight, and 

 to be prejudiced and retarded by strong light as well as by an 

 absence of illumination. This report, however, has been contra- 

 dicted both by Payen (I.) and Poggiale (L). A similar 

 observation to that of Pochard was made by A. Lendner with 

 regard to the formation of conidia in Aspergilhis luteus, Asp. 

 niger, and Bofri/fis (cinerea ?). Elfving (I.) states that the 

 formation of perithecia in Aspergillus glaucus is entirely or to 

 a large extent suppressed by light ; and the same applies to 

 the formation of the pileus in certain members of the genus 

 Coprinus — congeners of the mushroom — observed by Brefeld 

 (IIL). 



Nevertheless, the question of the influence of light on the 

 fructification of any given fungus cannot be answered off-hand. 

 On the contrary, it has been established beyond doubt that the 

 nature of the action exerted by light depends on the other 

 conditions of vitality, Brefeld (III.) having shown, in the case 

 of Coprinus stercorarius, that the formation of the pileus ceases 

 in the dark when the temperature remains below 15° C. This 

 discovery that light rays can be replaced by heat rays becomes 

 of greater interest when it is borne in mind that — as was de- 

 termined by Brefeld — the only light rays having any influence 

 on that development are the blue-violet ones, and not the less 

 refractive (e.g. the yellow) luys. A detei'minative influence 

 is also exercised by the composition of the nutrient substratum. 

 Thus, A. Lendner made the obsei'vation — which deserves follow- 

 ing up — that spoi'angiation in Mucor Ji avid us occurs in white 

 light, bvit ceases in yellow or red light or in the dark, when the 

 oi'ganism is grown in Raulin's nutrient solution (§231); but 

 that the converse is the case when van Tieghem's nutrient 

 solution is used. 



