STRUCTURE AND DEVELOPMENTAL RATE 223 



about this higher affinity for oxygen at one point than at another? 

 Certainly, we do not at present know! 



This unknown factor acting between the growing buds or em- 

 bryos when out of equihbrium, inhibits to an unusual degree the 

 rate of oxidation and through this probably the rate of cell- 

 multiplication, and certainly the rate of development in one of 

 the components. All the defects observed in the inferior com- 

 ponent are simply due to a slowing of its developmental rate or 

 are strictly what I have always termed developmental arrests. 

 This problematical factor, then, simply tends to lower the rate 

 of development in the one component and thereby does w^hat the 

 experimenter is able to do in various ways with any developing 

 single individual. I ('06, '07, '09, '10 a b, '13, etc.) have experi- 

 mentally produced in single embryos all of the deformities seen 

 in the smaller components by arresting the developmental rate 

 of eggs with a large number of different chemical and physical 

 treatments. Newman ('17) has observed exactly the same types 

 of monsters among slowly developing hybrids. As Newman very 

 correctly points out, one obtains similar monsters by any method, 

 either treating the eggs with injurious chemicals, strange physical 

 conditions, or by heterogenic hybridization. Each of these 

 methods simply lowers the rate of metabolism and the rate of 

 development. Newman, in agreement with my position, rec- 

 ognizes all of the monsters as being primarily due to a lowering 

 of developmental rate and, therefore, generally speaking, they 

 are actually developmental arrests. From an extensive study of 

 monstrous individuals, Dareste ('91) long-ago believed that all 

 developmental abnormalities were in general arrests, yet he 

 lacked proof for such a position. 



The present study, however, enables me to state the case in 

 far bolder and more definite terms than it has been possible to 

 do before. In the first place, every type of developmental monster 



Fig. 30 The terminal portion of a long privet stem which had grown upward 

 in a shaded position. On reaching direct sunlight the axillary buds three leaves 

 from the bottom of the figure grew into lateral shoots. Very soon after this the 

 axillary buds of the pair of leaves immediately below the first shoots give rise to 

 the second pair of lateral shoots, and finally the buds of the leaf pair immediately 

 above the first shoots grow into a third pair of lateral branches. In nine cases 

 this budding sequence was invariably followed. 



