1877. ] Botany. — 489 
and after many observations found that the relative numbers were as 
ninety stomata to the upper, and eighty-seven to the lower surface. A 
year later the average of three observations on older leaves gave as the 
relative numbers, sixty-two for the upper, and sixty-nine for the lower 
surface. Again, in 1874, averages of carefully made observations upon 
young leaves gave as relative numbers forty-nine for the upper surface, 
and fifty-nine for the lower. Observations made at the same time upon 
old leaves gave the numbers fifty-seven for the upper, and seventy-five 
for the lower surface. 
Now by comparing these results with the number of stomata in the 
leaves of other plants, we arrive at the value of the greater or less abun- 
dance of these on either surface as influencing the direction of the leaves. 
In 1872 I examined the leaves of the common sunflower (Helianthus 
annuus, var.) and found that the stomata of the upper surface were to 
those of the lower as 102 to 105. In 1874 I found after repeated ob- 
servations that the stomata on a cabbage leaf were as seventy for the 
upper surface to eighty-six for the lower... Now these numbers are so 
nearly like those found in Silphium, that we conclude that the mere 
number of stomata can have little if anything to do with determining 
polarity, for in both of these cases there is an utter want of it. I think 
we may then with reasonable safety throw the stomata out of the ques- 
tion for it is very doubtful if they alone have anything to do with it. The 
texture of the leaf must be more carefully examined than it has yet been 
to enable us to determine the real cause of the polarity. We know that 
some leaf surfaces, generally the upper — turn quickly and forcibly to- 
wards the sun, as is notably the case in the sunflower mentioned above ; 
the cause of this heliotropism we do not know: now if we conceive a 
leaf with its two surfaces endowed with this sensitiveness to light, or, in 
other words, if both sides are equally heliotropic, the leaf will, in the 
struggle of the two sides for the greater share of light, be compelled to. 
assume a position similar to that taken by the leaves of Silphium lacin- 
tatum ; but here we need further facts. — C. E. Bessey, Ames, Iowa. 
Precociry or BLOSSOMING IN THE ORANGE. — In general it takes 
the orange tree, in the most favorable localities in Florida, at least five 
years from the sowing of the seed to produce the flowers and fruit, and 
1 Adolph — ‘records i in Jahrb. fiir witsen. Bot. volume iv. 1865, that he toana 
the stomata n the two surfaces, namel 
Hants annuus, sppr r surface rD aidi soifa 325. 
l 
Bra ca oleracea. e 0 
Which differ E from my ror Hower, some of his other plants 
are almost equally good examples for 
Datura stramonium, ope er surface nia, under surface et 
Che eg a ides, * 156. 
Morren, in Bull. de dente Re yale d cae ‘i he following prog 
namely : — 
Trifolium fetes upper maos 207, unger wuriace 335. 
Helianthus 137, 242. 
