524 Chronicles of Science. [Oct., 



Greenwich records of this star, the following mean annual proper 

 motions in four several intervals : — 



Years. 



Proper Motion in R. A. 



Proper Motion N. P D. 



1845-1850 



.. .. +0 s -358 



+ 5"'82 



1850-1860 



.. .. 0-343 



5-73 



1860-1864 



.. .. 0-336 



5-93 



1864-1869 



,. .. +0-338 



+ 5-71 



We may fairly assume that the mean of these values (properly 

 weighted) represents the true value of the star's motion — which it 

 will be seen is exceptionally large. 



4. BOTANY. 



Evaporation of Water from Plants. — Some researches have recently 

 been undertaken by Yon Pettenkofer on the amount of evaporation 

 which takes place from the foliage of plants. The experiments 

 were made in the case of an oak tree, and extended over the whole 

 period of its summer growth. He found the amount of evapora- 

 tion to increase gradually from May to July, and then decrease till 

 October. The number of leaves on the tree were estimated at 

 751,592, and the total amount of evaporation in the year at 539 ■ 16 

 cubic centimetres of water for the whole area of the leaves. The 

 average amount of rainfall for the same period is only 65 cubic 

 centimetres; the amount of evaporation is thus 8 J times more 

 than that of the rainfall. The excess must be drawn up by the 

 roots from a great depth ; and thus trees prevent the gradual 

 drying of a climate, by restoring to the air the moisture which 

 would otherwise be carried off by drainage. 



Germination of Palms. — Mr. J. W. Jackson, Curator of the 

 Museum at Kew, has published a useful paper " On the Germina- 

 tion of Palms." This is incorrectly described in all the botanical 

 text-books commonly in use. The peculiarity consists in the end 

 of the cotyledon remaining in the seed, whilst its stalk is pushed 

 out, carrying with it the radicle, which germinates in the usual 

 manner at a little distance from the seed. In the double cocoa-nut, 

 Lodoicea, the protruded end of the cotyledon is as much as 12 

 or 18 inches long. The sheath or socket at the base of the stem 

 of this palm is shown not to be peculiar to it, as has been supposed, 

 though more developed than in other species, and to be formed by 

 the vascular bundles of the rudimentary and early leaves. 



Existence of a Formative Layer in the Leaves of Plants. — 

 M. Cave has recently pointed out that a formative layer exists in 

 the leaves of plants, similar to the well-known cambium layer, 

 which, in exogenous plants, intervenes between the bark and the 



