Dixon and Atkins — On Osmotic Pressure in. Plants, cVc. 286 



pressed them ; otliers reqiured to be somewhat broken up before the sap 

 would issue from them. Then it was necessary after the first crusliing to 

 open the vice, take out tlie crushed pellet, and loosen and crumple anew the 

 compressed mass of 'leaves witliin. On the second or third readjustment of 

 this sort the sap usually flowed freely from the crushed leaves. In tliis 

 manner sap was expressed more or less readily from all the leaves tried, with 

 tlie following exceptions : — 



(1) The leaves of Tilia micropliylla. — Only one sample of this tree was 

 tried, but from it could be obtained no more sap tliau would just moisten the 

 linen. 



(2) Shoots of Tliuja plicala also yielded extremely little sap, wliich, owing 

 to its very viscid nature, would not drop from the linen. 



(3) The buds of Syringa vulgaris, taken at the end of September, also 

 refused to yield any appreciable amount of sap. 



At tliat stage we were unable to devote the time to see if the difSculties 

 which prevented sap being obtained in these three cases could be surmounted; 

 and it remains to be ascertained whether, by more painstaking work, these, 

 too, can be got to yield sufficient sap, or whether the list of organs whicli 

 cannot be treated in this manner will have to be extended. 



When pressing the sap one cannot fail to be struck with tlie difference in 

 colour of the sap issuing from various leaves ; and one is astonished to find 

 intense coloration in. the pressed sap from leaves apparently of the purest 

 green. For example, the green leaves of Syringa vulgaris, Fraxinus excelsior., 

 F. oxypliylla, Catalpa bignonioides, Magnolia acuminata, all yield a sap more 

 or less intensely brown. In some cases — e.g. Syringa vulgaris — it is of such 

 a deep colour that it appears almost opaque when held up to bright day-light 

 in a small test-tube about 1 cm. in diameter. This coloration does not appear 

 to be due to oxidation, as it is observed in the drops as they issue from 

 the leaf. In some cases it intensifies on exposure to the air ; but this change 

 is a slow one. 



From other leaves the sap is of a greenish-grey hue — e.g. from the leaves 

 of Vitis (Ampelopsis) Veitchii, Pier is aquilina. This coloured sap is also 

 found in the green shoots of Equisetum Telmateia. 



Pale-green sap is found in Wistaria sinensis, Eucalyptus globulus, Pinus 

 Laricio, Cordyline australis, 0/iamaerop)s humilis, Iris germanica. In the case 

 of Vitis, Wistaria, and Eucalyptus, leaves which were evidently coloured by 

 anthocyan yielded a sap tinged with pink. Heliantlius muUiflorus was 

 remarkable in yielding an almost black sap. The sap of the roots examined 

 was of a paler hue in the ease of Syringa vulgaris than that of the leaves. 

 The roots of Eucalyptus yield an ochre-coloured sap. 



2z2 



