Nov. 1, 1925 
Fruit-bud Formation of Pear and Apricot 
875 
the first to appear. Walker 5 found differentiation started August 4 
(1916) under similar conditions. It is interesting to note that the 
buds of a given date and condition that were observed were of 
surprisingly the same stage of development. As pointed out by 
Henderson, 6 pear buds of a given collection varied widely in the stage 
of development. 
Little advance could be seen in the material collected August 21, 
as compared with that of August 10, except that the small protuber¬ 
ances or sepal primordia were more pronounced. However, by Sep¬ 
tember 2 considerable advancement had taken place. The sepals 
had pushed upward and inward at the top, forming a cup, while the 
whole bud had broadened, except at thelbase. Primordia of petals 
were present inside the cup. They arose from the inner surface of the 
cup or receptacle. Also, the pistil was prominent as a blunt swelling 
from the noor of the cut. By September 16 all parts had further 
enlarged, and in addition to the sepals and petals the outer whorl of 
stamens was present. By September 29 the second and third whorls 
of stamens were present and all were of apparently the same stage of 
development. At the same date, owing to this elongation, the petals 
were drawing together above the stamens. 
All parts continued to enlarge during October. By October 30 the 
petals, narrowly attached at the base, appeared lanceolate in section. 
Stamens were well differentiated into filament and anther, while in the 
four lobes of the latter pollen mother cells were observed. The pistil 
had elongated and the style could be distinguished from the broaden¬ 
ing ovary. The ovarian cavity was present, but as yet no ovules were 
evident. By December (pi. 5) the petals had completely inclosed 
the bud at the top and the buds were slightly larger. 
Buds collected January 1 showed a big increase in size of all parts. 
Ovule primordia were present as small knobs in the ovarian cavity, 
and the stigma had developed at the upper end of the lengthened 
style. A cross section of the ovary shows it not to be a perfect circle, 
but the walls fold in on one side, forming the future suture of the 
mature fruit. The ovules develop from the enfolded ends. 
During January the buds continued to enlarge. The development 
in the ovary was slow. The stamens became larger and by February 
6 had definite walls inclosing the large, rounded, loosely connected 
mother cells now ready for cell division (pi. 6). Material collected 
February 14 contained the four-celled or tetrad stage in pollen devel¬ 
opment. In apricots, as in pears, only one date snowed this stage. 
By February 21 pollen was mature, but development of the ovule had 
progressed very little, as can be seen from Plate 5, D. 
Following this stage, however, the development in the ovule pro¬ 
gressed rapidly, and only five days later the two integuments and the 
nucellus were plainly evident in longitudinal sections of the ovary 
(pi. 5, F). The buds rapidly expanded, and the tree was in full 
bloom by March 2. 
8 Walker, K. M. the formation and development of the fruit buds of the royal apricot. 1917. 
[Unpublished thesis, Univ. Calif.] 
8 Henderson, W. the differentiation and early development of the flower buds of the bart- 
lett pear. 1916. [Unpublished thesis, Univ. Calif. 1 
74333—26f-6 
