TEANSACTIONS OF SECTION D. 701 



This turgescfince appears to aris§ from root-activity continuing, after the transpira- 

 tion, or rather conducting, power of the leaf, for reasons hereafter noted, has been 

 in the main lost. The presence of water in the living cells of the absciss-layer is 

 so much the greater from their being bounded by cells which are practically dead ; 

 and whereas the rounding of two living cells in contact need not destroy their power 

 of cohesion, the rounding of a living cell in contact with one which is dead would 

 probably cause complete separation. 



The soft elements of the vascular bundles are eitherpinched, or else cell-division 

 takes place in them also. The lignified elements undergo changes, the nature of 

 which I am not yet able to explain satisfactorily, and then rupture with the strain. 



(2) The transfer of the cell-cordents from the leaf. — In leaves about to fall, 

 starch is always found in the sieve-tubes, mainly collected in cloudy, granular- 

 looking masses in the neighbourhood of the sieve-plates. With iodine these grains 

 do not stain violet, but brown or reddish-brown. The accumulation is commonly 

 'greatest on the leaf side of the sieve-plate. To be devoid of starch is usually the 

 first sign of a leaf being ready to fall. In all cases where tannin is present in the 

 leaf, it is present, and with the same distribution, in the fallen leaf. Tannin and 

 starch are especially abundant in what I will call the food-layer at the base of the 

 leaf-stalk, in which the absciss-layer and cork-layer are formed. In naturally fallen 

 leaves starch is rarely found, except right at the very base of the stalk, and then in 

 very small grains. Taking in all cases precautions against prematurely fallen 

 leaves, perfect nuclei are comparatively rare in fallen leaves, though in some cases 

 (e.g., Salishuria adiantifolia, Acer j^latanoides, Catalpa bignonioides, Quercus pedun- 

 culata, and Ficus Carica) perfect nuclei are general in blade and petiole. Cells 

 containing no nuclei have, however, very commonly a number of larger or smaller 

 irregidar fragments of proteid matter, staining deeply with ammonia-carmine or 

 methyl-green. In many cases, where the nuclei are apparently perfect, they show 

 manifest granularity, and often irregularity of outline. The evidence tends thus to 

 show that the nucleus, or at least the chromatin, is left behind in the empty cell, 

 the nucleus tending to what we will call ' disintegration,' as distinguished from 

 ' fragmentation ' or direct division, this latter being by no means a sign of the death 

 of the cell. Nor does disintegration bear any relation with the fragments of 

 nuclear substance found in many pollen-tubey which show no nucleus, nor with the 

 scattered small grains, which perhaps replace the nucleus in many Chroococcacese, 

 Nostocacese, &c. Perhaps a strict classification would require to divide the terms 

 * direct division ' from ' fragmentation,' botli possible in living cells. 



It is interesting to note in this connection that from the leaves of the few ever- 

 greens that I have thoroughly studied, starch is likewise usually absent in winter, 

 being transferred to the stem, the tannin, on the other hand, remaining behind. 



8. On an Apparatus for Determining the Rate of Transpiration. 

 By Professor W. Hillhouse, M.A., F.L.8. 



9. On the Cultivation of Beggiatoa alba. 

 By Professor W. Hillhouse, M.A., F.L.S. 



This bacteriad is especially foimd on decaying algse, &c., in sulphur springs and 

 waters receiving the refuse of factories. It is comparatively large, the threads 

 varying in thickness from 0-001 to 0-005 mm., and hence is very suited for labora- 

 tory purposes in teaching. Though normally in the form of segmented threads, 

 attached to a substratum, it illustrates the most modern conceptions of bacteriolo- 

 gists (Cohn, Zopf ), showing, in various stages of its existence, coccus forms, rodlets, 

 spirals, swarming movements, and even creeping movements, which much resemble 

 those of the oscillarians. For laboratory work it can be kept growing continuously 

 aiid with certainty upon fragments of india-rubber tubing in water, upon which it 

 will usually appear spontaneously after the lapse of a few months. 



