Nov. 1, 1925 
Fruit-bud Formation of Pear and Apricot 869 
sections were made for the cytological study of pollen and ovary 
development. Only sections showing the floral parts were retained 
and mounted. 
After the middle of September the hairs on the inner side of each 
bud scale became so numerous it was impossible to cut the pear buds 
embedded in paraffin. It therefore became necessary to employ 
“ Gibson’s rapid process ” of the colloidin method as described by 
Lee {11), Drinkard (3) was able to cut all collections of the Kieffer 
pear in paraffin, but it is the writer’s belief that the Bartlett has a 
greater abundance of hairs than the Kieffer. After the January 1 
collection it was possible to continue the paraffin method, since the 
flower-buds had then become large enough to permit the removal 
of the hairs without serious injury to the floral parts. 
RESULTS 
DIFFERENTIATION AND DEVELOPMENT OF FRUIT BUDS OF THE PEAR 
Fruit buds were found among the buds collected July 7, 1922, 
from a lightly pruned and irrigated pear tree on the university farm 
(interior-valley conditions). However, since these flower buds were 
only in the first stage of differentation, it can safely be said that the 
Bartlett pear began fruit-bud formation the first week in July during 
the 1922 season. This finding is in accordance with that reported 
by Henderson. 4 At this time the growing point of the bud had ceased 
to give off bud scales and had become elongated and flattened on top. 
In the course of the next 10 days this crown had lengthened materially^ 
and part of the specimens in longitudinal section showed the large 
terminal and two smaller lateral primordial flowers in the form of 
blunt protuberances (pi. 1). Each infant flower was subtended by 
a bract or modified leaf. It might be noted that the vascular system 
of the spur advances very closely with the elongation of the growing 
points and is lost sight of only near the tips. 
In the collection made July 31 many buds were cut in which the 
terminal primordium had developed into a cuplike receptacle by 
a growth of tissue from its edges. The side primordia did not show 
as great development, but some had small projections at the edge. 
The August 10 samples showed little advance, except that in a few 
cases small round swellings on the inner surface of the receptacle 
cup showed the start of petals in the terminal flower. The entire 
bud slowly enlarged during the following 20 days,, the primordial 
petals of the terminal flower became more prominent, and their 
beginnings became evident in the laterals. 
During September (pi. 2) the buds continued to enlarge slowly 
and the first whorl of stamens had their origin from the torus lining 
the inner side of the receptacle cup, immediately below the petals, 
and resembling the petals at the early stages. In nearly all cases 
the terminal primordial bud which was the oldest was the largest 
in size and farthest advanced. By October 30 the petals had length¬ 
ened and at least another whorl of stamens had made its appear¬ 
ance. It was not determined at what stage tjiis whorl could first 
be seen, although there appeared to be much the same arrangement 
4 Henderson, W. the differentiation and early development of the flower buds of the 
bartlett pear. 1916. f Unpublished thesis, Univ. Calif.] 
