482 TRANSFORMATION OF ENERGY 



pare the temperature income with the diffusion inflow in this case. No one, 

 however, would desire to defend the view that the direction of the diffusion 

 inflow determines the orientation of the long axis of the cell ; it is much more 

 probable that the plant reacts to unequal distribution of the stimulant, and 

 endeavours to place itself in such a position that all sides are in contact with 

 equal concentrations of the stimulant. This, however, cannot be directly 

 proved, because it is not possible to bring about stimulation on different 

 sides by different concentrations, without producing at the same time a 

 diffusion current. 



MiYOSHi investigated a large number of substances in different states of 

 concentration, and was able to prove that some were good attractive media, 

 others only moderately so, whilst others still, if stimulants at all, were repul- 

 sive. Repulsions, such as those exhibited by the cells of Fungi, have been 

 observed after treatment both with free organic and inorganic acids ; 

 they were also induced by alkalis, alcohol, certain salts, such as potassium 

 nitrate, magnesium sulphate, potassium and sodium tartrate, all in solutions of 

 weak concentration. That the successful media did not act equally well on all 

 Fungi examined is easily intelligible. The Hyphomycetes behave very hke each 

 other, but Saprolegnia, living as it does under very different conditions, reacts very 

 differently. Exact investigations on the behaviour of such Fungi as are extreme 

 specialists so far as their nutrition is concerned, are calculated to teach us much 

 with regard to the special phenomena of chemotropism. Generally speaking, 

 ammonium compounds, phosphates, peptone, asparagin, and sugar are good 

 attractive agents ; ammonium phosphate among inorganic compounds is espe- 

 cially so. The different types of sugar, prominently grape sugar and cane sugar, 

 are excellent attractives for Hyphomycetes, but Saprolegnia responds but feebly 

 to them. Glycerine and gum arabic act neither attractively nor repulsively, 

 which indicates that the chemical action does not depend only on the 

 nutritive value of the substance. This is especially clearly seen in the case of 

 potassium nitrate, which acts repulsively, although it is a nutrient in many cases. 



Apart from the specific action of the individual substance dependent on its 

 chemical constitution, the concentration in which the solution is presented is of 

 importance. Mucor stolonifer, for instance, reacts to a o-i per cent, sugar solution 

 in a positive manner but more markedly to a 2 per cent, solution, and the re- 

 action becomes more vigorous as the concentration is increased. At 15-30 per 

 cent, the response is less apparent, and at 50 per cent, a repulsive reaction ensues. 

 An exact determination of the critical concentration between positive and nega- 

 tive response is required, and experiment has yet to show what is the lowest con- 

 centration or liminal intensity which has a stimulating effect. The statements 

 as to repellent concentrations are very meagre, because very often before 

 repulsion takes place the plants have suffered injury. Miyoshi (1894a) records 

 the following results, however: — a 10 per cent, solution of ammonium phos- 

 phate was repellent in the case of Saprolegnia, while a 5 per cent, was still 

 attractive; a 3 per cent, solution of ammonium , chloride (doubfully lower 

 concentrations) was repellent to the same plant; a 50 per cent, solution 

 of cane sugar in Hyphomycetes and a 20 per cent, in Saprolegnia ; a 50 per 

 cent, grape sugar in Hyphomycetes and a 10 per cent, in Saprolegnia ; 

 a 20 per cent, beef extract in Saprolegnia and some Hyphomycetes but not in 

 Mucorinae. In the last case the action was doubtless due to the phosphates 

 present in the extract. The liminal values of the attractive solutions as 

 inducing stimulation were naturally lowest in the case of the best media. The 

 liminal value of meat extract is 0-005 per cent, for Saprolegnia, of grape sugar 

 o-oi per cent, for Mucor mucedo, and of ammonium nitrate 0-05 per cent, 

 for the same fungus. The determination of the liminal value for differ- 

 ences in concentration on opposite sides is obviously of greater importance 

 than the determination of the absolute liminal value, which cannot be 



