296 Progress in Science. [April, 1871. 



BOTANY AND VEGETABLE PHYSIOLOGY. 



Transpiration of Aqueous Vapour by Leaves. — Professor McNab, of Ciren- 

 cester College, has recently published the results of an important series of 

 experiments on this subject, confirming in a remarkable manner the statement 

 made some time since by MM. Prillieux and Duchartre, that plants absorb no 

 moisture whatever in the state of vapour through their leaves. The following 

 are the more important results obtained : — 1. Quantity of water in the leaves. 

 The mean of several experiments gave 63-4 per cent. 2. Quantity of water 

 removable by calcium chloride or concentrated sulphuric acid. This was found 

 to be from 5-08 to 6'og per cent, while the sun caused about the same quantity 

 — 5*8 per cent — to be transpired. The remainder, from 56 to 57 per cent, was 

 therefore determined to be fluid in relation to the cell-sap of the plant. 

 3. Rapidity of transpiration in sunlight, diffused light, and darkness. The 

 results given are — in sunlight, 3-03 per cent in an hour; in diffused daylight, 

 o'5g per cent ; in darkness, 0*45 per cent. 4. Amount of fluid transpired in a 

 saturated and in a dry atmosphere in the sun and in diffused daylight. In 

 sunshine the experiments gave 25-96 per cent in an hour in a saturated atmo- 

 sphere ; 20-52 per cent in a dry atmosphere; in the shade, none whatever in a 

 saturated, 1-69 per cent in a dry atmosphere ; thus again confirming the earlier 

 observations of M. Deherain, that in sunlight evaporation goes on equally in a 

 saturated as in a dry atmosphere. 5. Quantity of water taken up by leaves 

 when immersed in it. The mean of several experiments gave 4-37 per cent in 

 1 1 hours. 6. Quantity of aqueous vapour absorbed by leaves in a saturated 

 atmosphere. None whatever. 7. Differences in the amount of fluid trans- 

 pired by the upper and underside of leaves in the sun and in diffused daylight. 

 Under both circumstances the amount was found to be much larger from the 

 under than from the upper surface. 8. Rapidity of ascent of fluids in plants. 

 From 4 T 7 2 th inches in 10 minutes to 8 T 7 5 th inches in 70 minutes. In all these 

 experiments the plant operated on was the common cherry-laurel (Primus 

 laurocerasus), and the fluid used for testing the rapidity of the ascent was 

 lithium citrate, the presence of a very small quantity of which can be readily 

 detected by the spectroscope. 



The phenomena of cross-fertilisation and self-fertilisation are still attracting 

 much attention among botanists. Mr. A. W. Bennett details in the " Journal 

 of Botany" for October, a series of observations on British plants. Two sets 

 of facts have been especially observed, in particular by Darwin in this country, 

 Hildebrand in Germany, and Delpino in Italy, to favour cross-fertilisation in 

 hermaphrodite flowers ; the phenomena of dimorphism and trimorphism, and 

 the special arrangements which render it easier for the pollen to be brushed off 

 by insects visiting the flower than to fall on its own stigma. But, besides these, 

 another arrangement exists by which self- fertilisation is hindered, the single fact 

 that the stamens and pistil belonging to the same flower are frequently not 

 ripe, so to- speak, at the same time. The terms protandry and protogyny, used 

 by Hildebrand, are adopted by Mr. Bennett ; but instead of non-dichogamy, he 

 prefers synacmy for the simultaneous maturing of the two sets of organs. The 

 most frequent arrangement appears to be that the pollen commences to be 

 discharged from the anthers at a longer or shorter interval before the maturing 

 of the stigma. In some cases there still remains a certain quantity of pollen 

 in the anthers when the stigma is ready to receive it ; in other cases the anthers 

 have either withered up or entirely dropped off before fertilisation of the 

 ovules can possibly take place. Synacmy is nearly as frequent as protandry; 

 while protogyny is of far less common occurrence. The two extremes among 

 the species observed may be stated to be Campanula rotundifolia and 

 Scrophularia aquatica. 



