164 CHARLES R. STOCKARD 



will be very conclusively shown that double conditions and twin- 

 ning in nature are the result of an unusual budding process pro- 

 duced by an early interruption of developmental rate, and are not 

 connected with a separation of the primary blastomeres except 

 under experimental procedure. 



Before entering into the particular points of the present experi- 

 ments, it may be well to explain in some detail the writer's con- 

 ception of embryo formation and the general process of budding 

 in plants and animals. 



It has long been known that the notches around the border of 

 certain plant leaves, such as Bryophyllum, have the power under 

 certain conditions to bud and give rise to an entire new plant. 

 It is observed, however, that the new shoots, as a rule, arise from 

 only one or two notches instead of from many. Loeb ('16) has 

 performed most elucidating experiments on the budding phenom- 

 ena in these leaves. In the first place, although' in nature only 

 a few notches on any one leaf send out shoots at any one time, 

 yet Loeb has shown that there is a potential ability present in 

 every notch to form a shoot. This fact is demonstrated by cut- 

 ting the leaf into parts in such a way as to isolate each notch. 

 Following such an operation a tiny shoot grows from every one 

 of the isolated notches. It becomes evident, therefore, that not 

 only does each notch possess the potential ability to form a 

 shoot, but under ordinaiy circumstances this shoot-forming abil- 

 ity is suppressed in most of the notches by ths growth of shoots 

 from only one or a few notches. 



It was further found that almost any notch on the leaf could 

 be selected and forced to bud at the expense of the other notches 

 by simply suspending the leaf so that the selected notch dipped 

 into water. This suggests, of course, that ordinarily the condi- 

 tions for bud formation are not equally favorable in all notches 

 and, therefore, only a few shoots arise from a leaf instead of one 

 in every notch. These few then tend to suppress the origin of 

 buds from other notches. Does any such set of comparable con- 

 ditions exist in a developing egg or blastoderm before the initial 

 line or axis of the embryo arises and begins development to 

 form a cornplete animal? 



