POPULAR MISCELLANY. 



141 



per cent, in the course of a few days. Pro- 

 fessor Bohm's theory corresponds closely 

 with that advanced by Professor Draper in 

 his work on the circulation in plants and 

 animals, and substantially agrees with the 

 views of Herbert Spencer, as expressed in 

 his paper on " Circulation and the Forma- 

 tion of Wood in Plants " (" Transactions of 

 the Linncean Society," March 1, 1866). It 

 supposes that the sap-bearing cells in the 

 whole plants are subject to a moderate 

 pressure in consequence of the resistance 

 which the water meets on its way from the 

 root to the assimilating leaf. If, however, 

 the branch can take up water through a cut 

 end with little difSculty, a partial absorption 

 of the contents of the vessels into the sap- 

 bearing cells will follow, new water will 

 pass through the cut end from without into 

 the vessels, and the limb will become 

 heavier. In this process, the ducts of the 

 willow do not serve as air-tubes, but as 

 water-canals which pour their contents into 

 the pump-system of the sap-bearing cells. 

 These canals become obstructed, after the 

 cuttings have stood for some time in the 

 water, by the growth of cells across the 

 tubes. As soon as the flow of water through 

 the vessels to the Iiigher part of the limb 

 is thus interrupted, the rapid increase of 

 weight ceases. That the cutting does not 

 perish at this stage, but continues to live 

 for several months without any consider- 

 able increase of weight, is due to the fact 

 that after the ducts have been closed the 

 circulation of water takes place only through 

 the sap-bearing cells and is greatly retard- 

 ed. In another series of plants, as the 

 oaks, acacias, catalpas, amorphas, etc., the 

 ducts of the new wood have been found 

 to be penetrable to the air, but neither air 

 nor water could pass through the old wood, 

 because the older veins were closed by trans- 

 verse cells or gummy substances. The ves- 

 sels of these plants were really air-vessels, 

 for they held only air of the tension of the 

 atmosphere and were destitute of sap. Yet 

 an uninterrupted stream of sap must be kept 

 up in such plants from the root to the top. 

 It takes place in the same manner as in 

 willow-cuttings, the vessels of which have 

 been closed by transverse cells that is, the 

 sap is filtrated from cell to cell, so that the 

 balance in the pressure of the contents of 



the adjoining cells which has been disturbed 

 by transpiration is restored. It follows 

 from this that the tension of the air in the 

 upper sap-bearing cells must be very slight 

 to make a rising of the sap possible. The 

 exhaustion of the air finally reaches its ex- 

 treme degree at an appointed age of the 

 cells, the air in the cells is cut off from the 

 neighboring vessels, and the factor which 

 produces the rise of sap is thereby elimi- 

 nated. The wood, which was a living sap- 

 wood, becomes a dead heart-wood. This 

 process is accomplished with different de- 

 grees of rapidity in different kinds of plants ; 

 even in individuals of the same species, cir- 

 cumstances cause many differences in the 

 formation of heart-wood. The final result 

 is, however, always the same, the natural 

 death of the tree by debilitation. The thin 

 outside layer of living wood is no longer 

 sufficient to supply the expanded top with 

 fluid food, no formation of new wood worthy 

 of the name takes place, the limbs die out 

 year by year, and finally only a feeble shoot 

 here and there, with a few leaves of a strange- 

 ly light color, indicates that there is still a 

 little life in the stem, and this is destined 

 soon to be extinguished. Those trees whose 

 vessels continue to be filled with water in 

 their old age, as the willows, birches, lin- 

 dens, horse-chestnuts, etc., do not die in this 

 manner, but through a dissolution of their 

 sap-bearing vessels and wood-cells, opening 

 the way for the introduction of fungi-, which 

 settle within them and attack their sub- 

 stance. The process of decomposition spreads 

 and the wood is gradually reduced to dirt, 

 till the tree finally falls or is blown to the 

 ground. 



The French issoeiation. The French 

 Association for the Advancement of the 

 Sciences held its ninth annual meeting at 

 Rheims. The opening address was deliv- 

 ered by the President, M. Krantz, who re- 

 ferred to the growth of the Association 

 since its organization, just after the close 

 of the Franco-German war, and to the results 

 of the Great Exposition of 1878. The prog- 

 ress of the Association has been continu- 

 ous and marked from year to year, and it 

 now numbers thirty-one hundred and fif- 

 ty-six adherents. It has a capital exceed- 

 ing three hundred thousand francs, and 



