76 BOTANICAL GAZETTE | JANUARY 
. The more important results which he established are as follows: He 
finds an almost universal closing of the stomata of terrestrial plants during 
withering, though in almost all cases complete closure is delayed, and after 
several hours the stomatal transpiration still greatly exceeds the cuticular. 
The closure is usually preceded by a temporary opening, due to the dimin- 
ished epidermal pressure on the guard cells. This can be produced more 
readily in the morning before the stomata naturally open, but not at night 
after they are closed, and is especially noticeable in laticiferous plants. In 
many aquatics and marsh plants there is at least a partial closure upon 
withering, but as a class they do not close to the degree observed in land 
plants. In many cases where there is no apparent movement at first, closure 
sets in several hours after withering, and the author asserts his opinion that 
in no case are the stomata entirely immobile. That closure is correlated 
with diminished water supply is shown by the invariable closure when the 
stem is compressed in a vise, and opening when released. Dry air causes 
closure though the leaves show no signs of flaccidity, and in very dry air the 
closure is preceded by a prolonged “preliminary opening.’’ The stomata 
are opened by weak electric currents, but stronger shocks close them. In 
chloroform and ether vapor they close slowly and then open again, and in 
CO, they slowly close. In bright sunshine they are more widely open than 
in diffused light, and they close on dark stormy days even in summer.- Arti- 
ficial darkness usually produces closure, and opening occurs when again 
illuminated, but the time required in each case depends upon the time of day, 
the normal “daily period” being quite marked. Of the large number of 
unspecialized terrestrial species tested, only a small percentage do not close 
their stomata at night. Among nyctitropic plants, whether terrestrial or 
aquatic, the great majority do not close the stomata at night, and especially if 
the temperature be fairly high. Even among unspecialized terrestrials, 
Darwin considers that the closure is not so complete as to prevent transpira- 
tion, though it greatly diminishes it. He discusses at some length the ecology 
of nocturnal closure, but does not seem to think that we know enough about 
its effects to justify definite conclusions, though he considers the economy of 
water and of heat to be important factors. A strong tendency toward a daily 
periodicity is apparent, for much less light opens the stomata in the morning 
than in the afternoon ; conversely, it takes much longer exposure to darkness 
to close them in the morning than in the afternoon. Dry heat tends to ope? 
the stomata ; and of the visible spectrum the red rays are the most effective. 
The effect of prolonged darkness is to reopen the stomata. 
The question of the mechanism of the stoma is discussed at some 
length, and the author seems to think that it is in about the same condition 
in which von Mohl left it in 1856. As to the immediate cause of the move 
ment, he combines the views of Leitgeb and Schwendener, and holds that it 
