220 CHARLES R. STOCKARD 



buds and they grew equally, in the second and third cases one 

 bud occupied a position of advantage over the other; this advan- 

 tage may have been due to a slightly more favorable exposure 

 to sunlight, heat, or moisture, or to a better flow of sap material 

 on its side of the stem. Its more rapid rate of growth in some way 

 imposes an inhibiting influence on the expression of the other bud, 

 causing it to be smaller, sometimes ill-formed or suppressed 

 entirely. If the larger bud be pinched away in any of the cases, 

 the smaller immediately improves its condition" and grows large, 

 provided it has not been held back too long (figure 29 A, B 

 and C). 



The advantages of certain positions on a stem over others is 

 strikingly shown by privet branches growing in dense shade. 

 These branches are slender shoots with long intervals between the 

 pairs of leaves until finally they reach the sun. After a certain 

 length of the stem has grown into the sunlight, the axillary buds 

 of a particular pair of opposite leaves grow into shoots. Later, 

 when still further in the sun, the two axillary buds immediately 

 below those that grow first, now grow to form the second pair of 

 shoots. Still later the axillary buds from the leaf pair immediately 

 above the first shoots send out the third pair. I have observed 

 this exact order of growth in nine cases of shaded stems. The 

 first shoots to appear have an advantage of position over the 

 second and third on account of a proper exposure to sunlight and 

 at the same time occupying a certain distance away from the 

 growing tip. The second buds then come into sufficient sunlight 

 and grow out despite the inhibiting influence of the first pair, and 

 finally the third pair of buds now grow on account of having be- 

 come more mature and further removed from the growing tip. 



The two embryos developing from a single blastoderm compete 

 in a comparable way, and the results of the competition are also 

 similar to the case of the plant buds. In the present state of our 

 knowledge, it is impossible to say what the primary cause is that 

 gives one of the growing parts an advantage over the other. We 

 may merely express this in a non-committal way as an 'advantage 

 of position.' It would in no sense relieve our ignorance of the 

 situation to state the likely probability that one of the growing 

 points has a higher rate of metabolism or a more rapid oxidation 



