86 SUMMARY OP CURRENT RESEARCHES RELATING TO 



on the contrary, that all the different tissues may be adapted to this 

 special purpose. 



The process of the absorption of water he explains as follows : — 

 Transpiration attracts, so to speak, upwards the osmotic force, which 

 is met by the flow of sap from all the neighbouring parts of the stem, 

 especially in the elongated elements. The diminution of pressure which 

 results brings into play from below the turgidity of the stem and the 

 elasticity of the cortex ; this causes increased activity in the root, which 

 brings about an accumulation of water in the lower parts of the plant 

 and an increased elevation of the sap. Capillarity and air-pressure 

 play only a secondary part. 



Sap.* — J. Attfield gives an account of observations made on sap 

 exuding from a wounded silver birch tree. A branch 7 inches in 

 diameter, had been lopped off a tree 39 ft. high, about 10 ft. from the 

 ground, before the leaves had expanded, leaving a wound about an 

 inch in diameter, from which sap dropped. A bottle was suspended 

 so as to catch the sap, and from observations it was found that the 

 flow was apparently faster in sunshine than in the shade, and by day 

 than by night, and altogether amounted to about 5 litres a day ; this 

 had been running for 15 days, but how long it would continue is un- 

 certain. The sap was clear and bright, sp. gr. 1-005, had a faintly 

 sweet taste and a slightly aromatic odour. After 12 hours it deposited 

 a trace of a sediment, which, when examined microscopically, was 

 found to consist of parenchymatous cells and a few so-called sphere- 

 crystals. The liquid contained 99 per cent, water and 1 per cent, 

 solid matter, which was composed mainly of sugar, 91 per cent., the 

 other constituents being ammonium salts, albuminoids, nitrates, 

 phosphates, and organic salts of calcium and magnesium, mucilage, 

 and traces of nitrites and potassium salts. It had calcium and 

 magnesium salts in solution equal to 25 degrees of total permanent 

 hardness. It contained a ferment capable of converting starch into 

 sugar, and when exposed to the air, it soon teemed with bacteria, the 

 sugar being changed into alcohol. 



Solid Pigments in the Cell-sap. t — The petals of flowers are far 

 more often coloured by a pigment soluble in the cell-sap than by one 

 in a solid granular form. Of 200 species examined by P. Fritsch, 

 only 30 contained solid pigments in the cells either of the petals or 

 of the fruits. 



Far the most common of these solid pigments is yellow, much the 

 greater number of yellow flowers, including nearly all yellow Com- 

 positse, being indebted for their colour to substances of this nature. 

 Exceptional instances of soluble yellow pigments occur in the petals 

 of Dahlia va7'iahilis, Altlicea Sieheri, and Tagetes, and in the hairs of a 

 good many species. Solid yellow pigments are described in Impatiens 

 longicornu, where they vary greatly in size and form, TropcBolum 

 majus, where the various shades of colour in the flower are due to a 



* Pharm. J. Trans., xiii. (1883) pp. 819-20. Cf. Journ. Chem. Soc— Abstr., 

 xliv. (1883) pp. 1164-5. 



t Pringsheim's Jahrb. Wiss. Bot., xiv. (1883) pp. 185-231 (3 pis.). 



