118 Gelehrte Gesellschaften. — Sammlungen. — Botanische Gärten. 
The biology of the nocturnal closure is a subject which can 
hardly be discussed in a Condensed manner. It is suggested that 
the gaseous interchange of assimilation may reqnire widely open 
stomata, whereas respiration may be carried on with comparatively 
closed apertnres. If this is so, the stomata might be to a great 
extent shut at night, and an economy in the nse of water effected, 
withont detriment to metabolism. Observations are given to show 
that quite another effect is brought about by nocturnal closure. 
As long as the stomata are open, the transpiring leaf is considerably 
cooler than the dry-bulb thermometer, but at night it has almost 
the temperature of the air. In this way a saving of heat is un- 
doubtedly effected—but it is not easy to say whether it is sufficient 
to be of much practical importance to the plant. I am inclined 
to believe, from Sachs’ 1 ) experiments on the depletion of leaves,. 
that all saving of heat must be valuable, by preventing the 
checking of translocation which he observed. 
The mechanism of the stoma is another subject which doe& 
not lend itself to Condensed treatment. I have tried to point out 
that the stoma has been neglected in the modern reorganisation 
of plant physiology from the point of view of irritability. Some 
observes insist on the preponderant infiuence of the guard cells, 
while L e i t g e b in the same way exaggerated the importance of 
epidermic pressure, whereas the two factors should, as far as 
possible, be considered as parts of a whole and as correlated 
rather than opposed in action. I have also attempted to show 
how the stoma, like other parts of the plant may be supposed to 
react adaptively to those signals, which we usually call Stimuli. 
The attempt which I have made to rank the problem among the 
phenomena of irritability, is very tentative in character. I have 
ventured to put it forth because I am convinced that it is in this 
direction that advances will be made. 
Societe pour l’^tude de la flore franco-helv^tique (Societ^ pour l’£tude de la 
flore fran<jaise transform^e). Septieme bulletin. {Bulletin de l’Herbier Boissier.. 
Annee VI. 1898. Appendix No. IV. p. 1 —11.) 
Sammlungen. 
Dörfler, J., Der jetzige Tauschmodus und die Wiener botanische Tauschanstalt.. 
(Allgemeine botanische Zeitschrift für Systematik, Floristik, Pflanzen¬ 
geographie etc. Jahrg. IV. 1898. No. 6. p. 92—95.) 
Botanische Gärten und Institute. 
Elliott, L. B., Representative American laboratories. I. Cornell University. 
(Journal of Applied Microscopy. Vol. I. 1898. No. 2. p. 23—32. With fig.) 
q Arbeiten, 1884. 
