74 Bulletin 393 



The figures show that limbs with a light bloom have heavier spurs 

 than limbs with a heavy bloom, and that spurs with conducting tissiie 

 of a given diameter taken from the former limbs weigh more than spurs 

 with conducting tissue of the same diameter taken from the latter limbs. 

 The leaves produced on spurs from limbs with a light bloom have a notice- 

 ably greater area than those produced on spurs which have conducting 

 tissue of equal diameter but which were taken from limbs with a heavy 

 bloom. The average leaf surface of several equally vigorous spurs ob- 

 tained from these two sources was 125.34 and 86.51 square centimeters, 

 respectively. The leaf area was measured by a planimeter. 



RELATION BETWEEN WATER SUPPLY, LEAF AREA, AND PUSHING OF BUDS 



It is generally understood that an abundant supply of water is a factor 

 in producing large leaves. This was demonstrated by the following simple 

 experiment. A number of dormant apple twigs were divided into two 

 similar lots. The cut ends of the twigs were placed in beakers containing 

 water. In one lot the cuts were renewed every few days and in the other 

 lot they were renewed only seldom. The leaves of the former twigs were 

 noticeably larger than those of the latter. This difference in size may be 

 ascribed to the more abundant water supply obtained by the leaves on 

 the twigs that had their cut ends frequently renewed. 



A more elaborate experiment, which involved the forcing of water into 

 the cut ends of the twigs, likewise indicated that there was a relation 

 between the leaf surface and the water supply. The details of the appa- 

 ratus used for this demonstration are shown in fig. 5. Tompkins King 

 branches from three to four years old and approximately one meter long 

 were used. The leaves on the twigs that had water forced into their 

 bases were distinctly larger than those on untreated twigs. 



This experiment, which was carried on in duplicate and which was 

 repeated several times, yielded other results that may be of interest at 

 this point. The buds on the check twigs, which were standing in a jar 

 of water, opened about a week before the buds on the twigs that received 

 their water supply under pressure. The first buds to open on the latter 

 twigs were the small ones on relatively weak spurs. The first vigorous 

 buds to piish were those nearest the tops of the twigs. Droplets of sticky 

 material oozed from all of the larger buds, which were found at the end 

 of several centimeters of the previous season's growth. Similar exuda- 

 tions were observed on less vigorous buds produced on spurs arising near 

 the bases of the twigs. 



Apparently the delay in the pushing of buds was caused by excessive 

 water pressure. The resistance encountered by the water passing thru 



i8« 



