VENATION AND SENESCENCE OF POLYEMBRYONIC CITRUS PLANTS 315 
Table i. Percentage of germinating seeds of Citrus grandis producing polyemhryonic 
seedlings 
Total No. Seeds 
Used in Test 
Percentage of Seeds that Germinated Producing 
Total Per- 
cent Ger- 
minated 
Total Percent 
Producing Poly- 
embryonic 
Plants 
I Hypocotyl 
2 Hypocotyls 
3 Hypocotyls 
4 Hypocotyls 
888 
48.82 
37.8 
4.2 
92 
43-18 
The interesting facts to be noted, however, are that nearly half of the 
seeds which germinated produced more than one plant each, and that 
only four seeds out of the entire lot produced four seedlings each and the 
great majority produced but two each. 
Influence of Certain Factors on Venation 
Schuster (1908) has contributed more of real value as regards the effects 
of environmental conditions upon venation than any other writer upon this 
subject. Benedict (191 5) has verified some of these findings in respect to 
Vitis vulpina. Zalenski (1902) did not confine his comparisons to a single 
species, so that hereditary variations were not eliminated. All the work, 
however, published by these writers shows that there are certain variations 
attributable to environmental causes. These should, then, so far as pos- 
sible, be eliminated before a comparison of the venation of polyembryonic 
seedlings is undertaken. 
Uniformity in Size of Vein-islets in Different Parts of a Leaf 
Schuster (1908) points out that there is a marked uniformity in the size 
of the vein-islets in all parts of the leaf except near the midrib and at the 
apices. The shape of the vein-islets in leaves of the grapefruit varies 
greatly in different regions of the leaf. Near the midrib they are long, 
narrow, and rectangular, and gradually become more nearly circular toward 
the periphery. Here a coalescence of the secondary bundles occurs, and 
the vein-islets are quite circular. Because of this difference in shape it was 
thought advisable to make determinations as to the size of the islets in the 
regions of the periphery and of the midrib respectively. The results of 
these findings are summarized in table 2. Sixty leaves were examined and 
four determinations were made from each region in each leaf. Hence, the 
mean averages represent a total of 240 determinations. In every table 
following, the figures representing the size of the vein-islets of a single leaf 
are the averages of four determinations. 
The data show that the size of the vein-islets is independent of their 
shape or place in the leaf. Therefore, in later work, determinations were 
taken from either the periphery or the region of the mid-rib. 
