1 6 NOTES AND COMMENTS [january 



continuing his well - known researches on the conditions which 

 determine the reproductive processes in thallophytes, has recently 

 published (Jahrb. f. wiss. Botanik, Bd. xxxii.) a paper describing 

 the effect of environment on the formation of sporangia and 

 zygotes respectively in Sporodinia, one of the Mucorineae. This 

 mould is peculiar, in that both reproductive organs arise from 

 similar primordia, and, according to Professor Klebs, the determining 

 factor, other conditions being equal, is to be found in the amount of 

 transpiration taking place from the surface of the plant, and this in 

 its turn depends naturally on the amount of moisture present in the 

 surrounding air. So rigidly is this the case that in less than twenty- 

 four hours he was able to determine at will whether sporangia or zygotes 

 should be formed, simply by opening or closing the flasks in which the 

 fungus was cultivated on discs of carrot, or on plumjuice-agar, both of 

 which are soils suitable for its growth, though its natural habitat is 

 the decaying cap of the larger toadstools. So long as the relative 

 moisture within the culture chamber does not exceed 65 per cent, 

 sporangia alone are formed, while if it rises above 70 per cent zygotes 

 appear in increasing numbers till absolute saturation is reached. The 

 most favourable conditions for the formation of zygotes are found 

 in the stagnant layer of saturated air which always hangs over the 

 plants in a still atmosphere, and in which any evaporation taking 

 place from the surface of the hypha must be due solely to the 

 temperature of the living substance being slightly higher than that of 

 the surrounding medium. A current of air, even when nearly saturated 

 with moisture, disturbs this layer, and thus tends to promote the 

 formation of sporangia quite apart from any consideration of an im- 

 proved oxygen supply, which indeed appears to exert but little influence. 



The formation of zygotes seems to be unaffected by changes of 

 temperature between a minimum of 6° and a maximum of 26° C, so 

 long as the relative moisture remains constant, but above the higher 

 limit the increasing transpiration induces sporangial development at 

 the expense of zygote formation. 



The nutrition of the fungus also influences the formation of 

 reproductive organs. Thus starvation promotes the development of 

 sporangia, not as might be expected of zygotes, and the same result 

 follows the employment of such purely nitrogenous food materials as 

 peptone, albumin, etc. On the other hand, certain carbohydrates 

 such as cane-sugar, maltose, glycerine, dextrine, etc., favour the 

 production of zygotes, while other substances belonging to the same 

 series, like arabinose, lactose, inuline, etc., promote the formation 

 of sporangia alone. The addition of peptone to the above-mentioned 

 carbohydrates does not in most cases influence the result. The acid 

 salts of certain organic acids, especially acid malate of ammonia, tend to 

 the production of zygotes, while the neutral salts of the same acids 

 promote only vegetative growth. 



