Correlation 101 



vegetative bud at maturity is proportional to the size of its subtending 

 leaf, suggesting a nutritional relation. Champagnat (1955 and other 

 papers) presents evidence that there are several distinct stimulating or 

 inhibiting influences that the leaf exerts on its bud. Snow and Snow 

 (1942), on the basis of experiments at the meristem, believe that an axil- 

 lary bud is determined by the primordium of the leaf that subtends it, 

 particularly the basal part. If the primordium is partially isolated from 

 the stem apex, its bud grows larger than it otherwise would. 



Related structures often affect each other. The cotton boll and its seeds 

 will not reach normal size if the involucre of the flower is removed 

 (Kearney, 1929). Knapp (1930) reports that the perianth of a liverwort 

 grows only if the archegonium that it covers is fertilized. The ovary in 

 most plants will not grow into a fruit unless at least a number of ovules 

 are forming seeds. These developing parts produce substances, appar- 

 ently, that stimulate the ovary wall to grow. This stimulation can be 

 imitated by the use of certain synthetic growth substances to produce 

 parthenocarpic fruits (p. 378). In case of metaxenia (p. 407), where the 

 male parent has a direct effect on the character of the fruits, this pre- 

 sumably results from something introduced through the pollen tube. 



Inhibitory Correlations. There are many developmental relationships 

 which are just the reverse of stimulatory and in which one part inhibits 

 the growth of another by some other means than competition for food. 

 These relations, like those of stimulation, commonly involve the action 

 of auxin and related substances. 



The best known case of such inhibition is the dominance by a terminal 

 bud which prevents the growth of lateral buds below it (p. 386). Simi- 

 larly, the epicotyl and its bud, in seedlings like those of beans, inhibit the 

 growth of buds in the axils of the cotyledons. Often a leaf can be shown 

 to inhibit the growth of the bud that it subtends, for if the inhibiting 

 organ is removed, the bud will then grow. Sometimes physiological iso- 

 lation has the same effect as removal. Child ( 1919, 1921 ) chilled a portion 

 of a bean epicotyl and found that the cotyledonary buds then began to 

 grow. Shading a leaf sometimes results in removing its inhibiting in- 

 fluence. 



Preventing the growth of the apical bud by encasing it in plaster some- 

 times has the same effect as removing it. Many of the early studies in 

 growth correlation involved this plaster technique (see Hering, 1896). 

 For example, if the portion of pea epicotyl between the terminal bud and 

 the cotyledons is so encased that it cannot grow in width, growth in 

 length is much reduced as compared with the control. 



Nutritional factors may have something to do with the inhibition of 

 cotyledonary buds, for Moreland ( 1934 ) observed that in bean seedlings 

 the growing foliage leaves have a greater inhibiting effect on these buds 



