72 



Bulletin 393 



The advantages of having a basis for estimating the probable set are 

 numerous. For example, plant breeders working on the apple might 



save considerable time and secure a higher 

 percentage of set if they confined their 

 work of cross-pollination to the vigorous, 

 many-flowered spurs that have made sev- 

 eral centimeters growth during the preced- 

 ing season. 



RELATION BETWEEN WEIGHT OF THE NEW 



SPUR GROWTH AND DIAMETER OF THE 



CONDUCTING TISSUE 



In cutting off the spur growth just pre- 

 vious to weighing, it was observed that the 

 diameter of the cylinder of conducting 

 tissue varied between i and 2 . 5 millimeters 

 (fig. 4). Closer inspection showed that the 

 spurs with conducting tissue of large di- 

 ameter had a greater leaf surface than 

 spurs with conducting 

 tissue of smaller di- 

 ameter. The weights 

 of new spur growth, 

 together with the di- 

 ameters of the con- 



.' A 



■----B 



Fig. 3. LEAVES and flowers on 



SPURS OF DIFFERENT VIGOR 



Lower figure, a typical vigorous spur of 

 the variety Tompkins King; upper figure, 



a spur below medium in vigor, of the same A..r-\\r\a ficciiA nf fViP 



variety. The spurs were obtained just >-iu(_Liii^ Uissuc ui uic 



before the flower buds opened. The num- „„,,-„ o-rc criiT-^n in 



ber of flowers (A, A'), the number and opurb, are given in 



size of the leaves, and the length of the foKlpo-? TViP Tnnfprifll 



precedmg years spur growth (B, B'), LdUie^y. 1 lie IlldLeildl 



may be compared. (J natural size) ^^^^ ^^^ f^^^ ^ ^^^^^ 



limb on a Tompkins King tree. All flower-bearing 

 spurs on the limb were considered. 



The weights of the spurs show a relation to the 

 diameters of the cylinders of conducting tissue. 

 The smaller the conducting tissue is in diameter, ^'cY^;f,DERs°iN'spuRs 



OF DIFFERENT VIGOR 



Cross section of a vigor- 

 ous spur, below, and of a 

 moderately vigorous spur 

 above. A, pith; B, xylem 

 (conducting tissue) ; C, cor- 

 te.x. The section was ob- 

 tained just above the ring 

 of scars. Outline from ca- 

 mera lucida drawing. X 6 



the lighter is the new spur growth. 



It should be noted that spurs with conducting 

 tissue of large diameter are sometimes produced 

 from buds that were terminal to less than one cen- 

 timeter of spur growth. In all such cases, however, 

 the spurs are large, in accordance with the preced- 

 ing data. Likewise, when spurs show relatively small conducting-tissue 

 cylinders, they are usually light in weight even tho they arise from buds 

 terminal to several centimeters growth. 



i86 



