PRESIDENTIAL ADDRESS. 625 



This is a much more detailed experiment than those of Stand fuss, Merrifield , 

 and Fisher, and it shows that the changes produced by the action of altered condi- 

 tions on the maturing germ-cells were definite and discontinuous, and therefore 

 of the nature of mutations in De Vries' sense. 



In another experiment Tower reared three generations of decemlineata to best 

 the purity of his stock. He found that they showed no tendency to produce 

 extreme variations under normal conditions. From this pure stock seven males 

 and seven females were chosen and subjected during the maturation periods of 

 the first two batches of ova to hot and dry conditions. Four hundred and nine 

 eggs were laid, from which sixty-nine adults were reared, constituted as follows : 



Twenty (12 <J,S ?) . . . apparently normal decemlineata. 



Twenty- three (10 6* .13 J) . . pallida. 



Five (2 (J, 3 ? ) . . . . iminaculothoivx. 



Sixteen (9 6*. 7 ? ) . . . . albida. 



These constituted lot A. 



The same seven pairs of parents subjected during the second half of the repro- 

 ductive period to normal conditions gave 840 eggs, from which were reared 123 

 adults, all decemlinealas. These constituted lot B. The dece.mline.atas of lot A 

 and lot B were reared side by side under normal and exactly similar conditions. 

 The results were striking. From lot B normal progeny were reared up to the 

 tenth generation, and, as usual in the genus, two generations were produced in 

 each year. The decemlineat.as of lot A segregated into two lots in the second 

 generation. A' were normal in all respects, but A 2 , while retaining the normal 

 appearance of decemlineata, went through five generations in a year, and this for 

 three successive years, thus exhibiting a remarkable physiological modification, 

 and one without parallel in nature, for no species of the genus Lcptinotarsa are 

 known which produce more than two generations in the year. This experiment is 

 a sufficient refutation of Weismann's argument that the inheritance of induced 

 modifications in Vanessa urticce is only apparent, the phenomena observed being 

 due to the inheritance of two kinds of determinants — one from dark-coloured 

 forms which are phyletically the oldest, and the other from more gaily coloured 

 forms derived from the darker forms. There is no evidence whatever that there 

 was ever a species or variety of potato-beetle that produced more than two, or at 

 the most, and then as an exception, three broods in a year. 



The modified albinic forms in this last experiment of Tower's were weakly ; 

 they were bred through two or three generations and came true to type, but 

 then died out. No hybridisation experiments were made with them but in other 

 similar experiments, which I have not time to mention in detail, modified forms 

 produced by the action of changed conditions gave typical Mendelian characters 

 when crossed with unmodified .decemlineatas, thus proving that the induced 

 characters were constant and heritable according to the regular laws. 



1 have thought it worth while to relate these experiments at some length, 

 because they seem to me to be very important, and because they do not appear 

 to have attracted the attention in this country that they deserve. 



They are confirmed to a very large extent by the experiments of Professor 

 Klebs on plants, the results of which were published this summer in the Croonian 

 Lecture on ' Alterations of the Development and Forms of Plants as a Result of 

 Environment.' As I have only a short abstract of the Croonian Lecture" to refer 

 to, I cannot say much on this subject for fear of misrepresenting the author ; but, 

 as far as I can judge, his results are quite consistent with those of Tower. 

 Sempervivum funckii and S. acuminatum were subjected to altered conditions of 

 light and nutrition, with the result that striking variations, such as the trans- 

 formation of sepals into petals, of petals into stamens, of stamens into petals and 

 into carpels, were produced. Experiments were made on Sempervivum acumina- 

 tum, with the view of answering the question whether such alterations of flowers 

 can be transmitted. The answer was in the affirmative. The seeds of flowers 

 artificially altered and self-fertilised gave rise to twenty-one seedlings, among 

 which four showed surprising deviations of floral structure. In two of these 

 seedlings all the flowers were greatly altered, and presented some of the modifica 

 tions of the mother plant, especially the transformation of stamens into petals 

 These experiments are still in progress, and it would perhaps be premature to 



