Physiologie. — Palaeontologie. 429 



of error encountered in ihe use of the instrument. These are 1) 

 the mechanical strain on ihe leaf due to reduced pressure, 2) the 

 passage of the air stream through the leaf, and 3) the effect of shock 

 in affixing the leaf Chamber. The first ma}' be disregarded when 

 using only low pressure differences of the same value throughout 

 the experiments. The second was variable in its effects on different 

 leaves, some being unaffected whilst others, like Begoriia, shewed 

 partial closure of the stomata. This error may be reduced lo a 

 minimum by stopping the air current between two readings and by 

 reducing the time occupied in taking a reading as far as possible. 

 The third source of error is also variable, Begonia leaves being 

 unaffected by handling, whereas those of Eiicharis regularh^ closed 

 their stomata when the Chamber was aßixed. In this case the sto- 

 mata re-open in less than two hours. 



The resistance offered by the intercellular Spaces of the leaf to 

 the passage of air is discussed. The stomata on different parts of 

 the same leaf are lound to behave simiiarly under approximately 

 similar conditions, but stomata on raature healthy leaves may open 

 more widelv than those of a verv voung or very old leaf. 



' E. M. Delf. 



Laidlaw, C. P. G. and R. C. Knight. A Description ofa 

 recording Porometer and a note on Stomatal Beha- 

 viour WiUing. (Ann. Bot. XXX. p. 46—56. 1916.) 



The authors describe a self-recording form of the aspirator 

 porometer already described by one of them. A head of water in a 

 constant pressure aspirator is employed to draw air through the 

 leaf, and the speed of the air stream (and therefore the relative size 

 of the stomatal apertures) is measured bj^ the rate at which water 

 drops from the aspirator, the frequency of the drops being deter- 

 mined graphicall}^ by a recorder. 



By means of experiments with this apparatus, the authors con- 

 firm the assertion of Darwin and Pertz, that on severing a leaf 

 from a stem, there occurs a temporary opening of the stomata prior 

 to the closure following upon wilting. The time elapsing between 

 the severing of the leaf and the opening movement varies with the 

 rate of wilting; with a thin leaf, such as Phaseohts, the opening 

 occurs ver}^ shortl}'- after the leaf is cut from the plant, w^hilst in a 

 thick leaf such as Eucharis Mastersi, the opening may be long 

 delayed. If the petiole is cut below the surface of water and kept 

 supplied with water, the temporary opening does not occur; this 

 Supports the Suggestion of Darwin that the closure is due to the 

 incipient wilting of the epidermal cells reducing their pressure on 

 the turgid guard cells and thus allowing them to expand somewhat 

 and increase the size of the stomatal pore. E. M. Delf. 



Potonie, R., Ueber die Diathermie einiger Carbon- 

 „Farne". (Beih. bot. Cbl. 1. XXXII. p. 468—475. 5 A. 1 F. 1915.) 



Verf. hat aus mehreren inkohlt erhaltenen Pflanzenresten des 

 Carbons Epidermen gewonnen in der Weise, dass er die abge- 

 blätterten oder noch auf dem Gestein befindlichen Kohlenteilchen 

 mit dem Schulze'schen Mazerationsgemisch und mit verd. Am- 

 moniak behandelte. In einigen Fällen hat er auch Wasserstoffsuper- 

 oxj'd benutzt. 



