888 
Journal of Agricultural Research 
Vol. XXIII, No. ii 
in one of the individuals the increasing length of day had initiated develop¬ 
ment of a flowering stem. These plants were then restored to the 7-hour 
day length. In the plant which had begun the development of a stem, 
elongation of this stem was soon checked, the final height reached being 
only 24 inches (PI. 3, A). This is in spite of the fact that the root had 
attained a diameter of nearly 5 inches. Final features of development in 
this interesting plant, as shown in Plate 3, B, will be considered under the 
subject of branching (p. 899). In spite of the large quantity of carbohy¬ 
drate material stored in the root the height of the stem was sharply 
limited by the duration of the light period. The beet (Beta vulgaris L.) 
differs from the radish in that it usually behaves as a biennial and Klebs 
(jj, p. 292) showed several years ago that this plant may be unable to 
flower the second season if kept in a warm greenhouse through the winter. 
Large roots which had been stored in an outdoor pit during the winter 
were set in soil and one lot placed under a io-hour day on April 1. The 
control plants under natural day length flowered late in June as indicated 
in Plate 8 , B. Under the io-hour light period elongation of the stems 
soon ceased and the apical buds developed into leaf rosettes. The io-hour 
day was so far below the optimum for apogeotropic development that 
foreshortening apparently was too abrupt to permit of flowering. The 
final result of the short-day conditions was that aerial “ beets ” (thickened 
stems) were formed at the bases of the leaf rosettes. Referring back to 
the behavior of tropical sorghums (Table I), it may be noted that a day 
length of 13 hours approximates the optimum for apogeotropic response 
in some of these varieties, as for example in S. P. I. 43626. After the 
flowering stage had been reached the final heights under the 13-hour day 
were decidedly in excess of those under the full day length or the io-hour 
day. The full day length evidently is excessive, while the io-hour day is 
less favorable than the 13-hour day. 
Preliminary observations on the growth of the apple (Malus sylvestris 
Mill) in contrast with that of Acer negundo L., for example, under different 
day lengths are of special* interest. As will be seen by reference to Plate 
4, B, seedlings of the latter are scarcely able to grow at all under a io- 
hour day. In marked contrast, the apple grows more rapidly under a 
io-hour day than under the full day length of midsummer. Young 
seedlings under the two light exposures are shown in Plate 4, A. Two 
specimens of standard Baldwin grafts and one of Baldwin grafted on a 
Paradise dwarf stock which were transplanted to large tubs in April and 
exposed to 12 hours of light daily soon began a rapid rate of growth 
which was maintained throughout the summer (PI. 5, A). Of the three 
corresponding individuals similarly transplanted but exposed to the full 
daylight of late spring and summer, only the graft on Paradise stock 
survived, and up to August this grew much more slowly than the trees 
exposed to a 12-hour day. During August, however, it was seen that 
there was marked acceleration in the rate of growth of the control, con¬ 
tinuing through early fall which, of course, is in line with the normal be¬ 
havior of the apple. To arrive at the full significance of these results 
will require further study, but they seem to indicate that the long days 
of midsummer occurring in high latitudes are distinctly suboptimal for 
apogeotropic vegetative development in the case of the apple and there¬ 
fore probably conducive to the initiation of flower-bud formation. As 
the tropics are approached the shorter length of the summer day would 
favor vegetative activity at the expense of flower-bud formation. 
