164 HAROLD H. PLOUGH 



The facts with regard to stimulation to parthenogenetic 

 development by high and low temperatures should be recalled 

 in this connection. Greeley in 1902 found that a relatively 

 long exposure to low temperatures — 0°C. to 6°C. — had a marked 

 activating effect on the eggs of Asterias. R. S. Lillie, in 1908, 

 showed that a similar effect resulted from a momentary exposure 

 to high temperatures — 30°C. to 35°C. These facts have been 

 recently confirmed by Lillie ('17) in connection with his butyric 

 acid treatment. Between 8°C. and 28°C. little stimulating 

 effect is noted. Lillie states his conclusions with regard to these 

 facts as follows: 



In this case of high temperature (above 30°C.) the activating influence 

 is probably to be referred to structural changes in the protoplasmic 

 system, as the temperature-coefficients indicate, and the same appears 

 to be true of cold. Changes in the physical condition of the structural 

 colloids, e.g., gelation, dehydration, altered aggregation-states, may 

 alter locally the permeability or other properties of the protoplasmic 

 system (e.g., of membranes or other barriers to diffusion) and thus 

 render possible interactions which are not possible at ordinary temper- 

 atures (Biol. Bull., March, '17). 



Whether this work has any bearing on the problem in hand, 

 is an open question. In any case the long series of studies on 

 Drosophila from this laboratory have shown beyond a doubt 

 that the chromosomal mechanism is responsible for the cross- 

 ingover phenomenon. One does no more than restate the facts, 

 therefore, in concluding that an environmental influence, tem- 

 perature, which .probably causes some alteration in the physical 

 basis of the egg has a definite measurable effect on the nuclear 

 phenomena in the developing egg. Just what this effect is and 

 what clue it gives to the nature of the crossingover process, future 

 research may show. 



Failure of heat to cause crossingover increase in presence of 'little 



crossover' modifier 



Before passing on to an analysis of the extent of the temperature 

 effect, it will be of interest to record one case in which a tem- 

 perature of 13.5°C. was absolutely ineffective in causing an in- 



