322 SUMMARY OF OUKRKNT liESEAKCHE.S KKLATING TO 



partially closed stomata, but also to a very slight extent through the 

 closed stomata. The greatest diffusive capacity was found in Eichhornia 

 and the night-diffusion of this plant was about 75 p.c. of its day-diffusion. 

 Allium and Oenothera showed only half this diffusion, and Fimlua and 

 Isatis only a fourth. It was shown that the stomata on the upper 

 surface of the leaf open and close more rapidly or close more completely 

 than those on the lower surface. 



H. Molisch* has experimented upon a large number of plants, as to 

 the conditions of the opening and closing of stomata. The author has 

 invented a new method for conducting such experiments, viz. an in- 

 filtration method. A substance capable of entering very minute capillary 

 openings, such as those of stomata, is placed on the epidermis of the 

 leaf ; this rapidly penetrates into the spongy parenchyma, causing im- 

 mediate infiltration of the latter. When viewed under the Microscope, 

 such infiltrated tissue appears dark in direct light and transparent in 

 transmitted light, and its condition is unaltered by subsequent closing 

 of the stomata. Al)solute alcohol may be used, but benzol, xylol or oil 

 of turpentine are far more sensitive reagents. The author finds that 

 most land-plants have a tendency to wholly or partly close their stomata 

 at night, but a few, such as Gucumis sativus, Ranuculus acris, and 

 3ielandrmm albam keep their stomata wide open at night, also many 

 bog and water plants, e.g. CaJflia palustris, Alisma Plantago, etc., but 

 results vary greatly with temperature, wind, humidity of air, etc. 

 Similarly when the leaves are fading, most land-plants wholly or partly 

 close their stomata, but a few, like Syringa vulgaris, open their stomata 

 wider at first, then partly close them, and finally open them to their 

 utmost extent. The greatest variations are seen in bog and water-plants. 

 The author believes that his new method will ])e of the greatest service 

 in clearing up some of the difficulties connected with this subject. 



Irritability. 



Colour-changes in Flowers.f — H. Fitting has studied the changes 

 in colour exhibited by flowers under different conditions. The present 

 work deals chiefly with the Geraniacea3, but also includes members of 

 other families ; the chief results are as follows : — The blue flowers of 

 Erodium gruinum and E. ciconium change their colour when warmed ; 

 at low temperatures, e.g. 20° C, they are blue, at higher temperatures 

 purple to rose-coloured, and at very high temperatures almost colourless. 

 A distinct tone of colour corresponds to each temperature. Sudden rise 

 of temperature induces corresponding sudden change of colour, but 

 colour cannot be regained so quickly as it is lost ; there is a definite 

 relationship between the times required for loss and restoration of color. 

 These colour-changes show a great similarity to the chemical changes 

 accompanying phenomena of irritability, viz. an almost instantaneous 

 beginning followed by a continual change until a certain equilibrium is 

 reached. Similar colour changes occur in dead petals and in water or 

 alcoholic extracts of these petals, but in these cases there is no definite 

 connexion between the times required for loss and restoration of colour. 



• Zeitschr. Bot., iv. (1912) pp. lOG-22 (2 figs.), 

 t Zeitschr. Bot., iv. (1912) pp. 81-105. 



