47 



regarded as the co-ordinated resultant oi the activities of the host 

 and parasite each, within the limits of its hereditary constitution, 

 being modifiable by the environment. Lines of comparative 

 research in animal and plant pathology are suggested. 



XLVIII. J. Hknderson Smith. "The Killing of Botrytis by 

 Heat, with a Note on the Determination of 

 Temperature Co-efjicients." Annals of Applied 

 Biolog^y, 1923. Vol. X. 



When a mass of spores of Botrytis cinerea is exposed to the 

 action of moist heat by immersion in water, the individual spores 

 are not all killed simultaneously. A few die quickly, a few after 

 prolonged exposure, and the majority at intermediate periods. 

 The whole process, when the numbers dead at successive intervals 

 of time are plotted against the time, g^ives a smooth curve, of 

 sigmoid and approximately symmetrical shape. The higher the 

 temperature used, the more quickly does the reaction proceed ; 

 but at all the temperatures examined, ranging from 37° C. (where 

 8-10 hours are necessary for its completion) to 50° C. (where the 

 last spore is killed in about 180 seconds) the curve has the same 

 shape, and the process is exactly the same, except for the change 

 in speed. In this respect the action of heat differs from that of 

 phenol, where the shape of the curve changes progressively as the 

 strength of phenol is raised, from the sigmoid type into a J-type 

 and eventually into a strictly logarithmic curve. The difference 

 is assigned to the occurrence with phenol of a stage of penetration, 

 during which the poison is making- its way through the external 

 coat of the spore, a stage which is absent in the case of heat. 



The shape of the curve agrees excellently with a recognised type 

 of frequency distribution, and can be adequately and reasonably 

 explained by supposing- that the individual spores differ in their 

 susceptibility to the action of heat. 



The effect of temperature on the velocity of the reaction is 

 unusually great, and is well expressed by the formula of Arrhenius, 

 if the temperature is reckoned from 0° C. instead of from the 

 absolute temperature. By combination of the formula for the 

 curve and the formula for the temperature-velocity relationship, 

 it is possible to express completely for the spores of Botrytis the 

 whole of the killing process within the limits and under the 

 conditions used in these experiments. 



XLIX. J. Henderson Smith. "On the Apical Growth of 

 Fungal Hyphce.'' Annals of Botany, 1923. 

 Vol. XXXVII. pp. 341-343. 



The fung-al hypha grows in length exclusively at the tip, and 

 the portion of the hypha behind the extreme tip never elongates 

 after it is once formed. This was determined by direct measure- 

 ments in a series of fungi selected from widely separated and 

 representative genera, and may be taken as a g-eneral rule applic- 

 able to all, or at least to most, fungi. In algae, growth may be 

 apical or may be intercalary ; in filamentous bacteria it is inter- 

 calary, each segment elong-ating for itself and at the same rate as 

 the others. 



