320 Profs. Percy Frankland and Marshall Ward. 



tion the whole time) was 30 p, long ; its growth in length was 

 recorded every 15 to 80 minutes or so, and the temperature as shown 

 by a thermometer by the side of the cultures noted. 



After allowing the growth to go on for 1 hours in the red, I 

 changed the glasses, and put the blue ones here and the red ones on 

 the other culture ; after growing thus for 2| hours, the exchange to 

 the original glasses was made again. 



The blue culture was started three-quarters of an hour later than 

 the red, a rodlet of almost the same length (31'5 /A) being selected 

 for observation. , 



After being half an hour under the blue glasses, this was changed 

 to red, and allowed to grow in red light for 2^ hours. 



The result was not sufficiently decisive to encourage my drawing 

 any conclusion. It is true the rod growing under red glass seemed 

 to have got a good start, so that its ultimate sojourn in blue light 

 was less injurious than might, perhaps, have been expected ; while 

 the shorter stay of the other in blue light appeared nevertheless long 

 enough to have affected it seriously. But meanwhile other factors 

 complicated the matter, and I discarded this line of experiment. 

 Before passing to the further developments, however, it will be well 

 to see what the foregoing results amount to. 



1. It is clear that growth occurs with increasing rapidity in suit- 

 able food materials and under suitable conditions, and is evidently 

 intercalary. Since it comes to an end eventually, the curve must be 

 that of a long drawn out _/~. 



2. The measurements show, also, that the rate of growth may 

 vary owing to the action of certain factors, partly external and partly 

 internal ; and these variations may be local in a filament, or general. 



3. The experiments show that the growth is slower on exposure to 

 sunlight (and may even be stopped altogether) passing through 

 certain screens, whereas it is not retarded perceptibly in light through 

 other screens. 



4. The results obtained so far, however, do not decide with cer- 

 tainty how far the differences with groiving 'filaments depend on other 

 factors than the light ; though they are pretty definite as regards the 

 spores, exposed in a resting condition. They even suggest that there 

 may be differences in the two cases e.g., that the actively growing 

 filaments may have some power of overcoming the detrimental action 

 of rays which seriously injure, or even kill, the spores in a state of 

 rest. 



5. It may be added that there is no question that exposure to 

 direct sunlight kills both spores and filaments ; numerous trials have 

 proved that. The question under investigation is rather how far 

 lower intensities of light are efficacious in this respect. So far the 

 measurements did not satisfactorily prove conclusively that active 



