- i7i their Structure and Functions. 411 



and exert the same power, as the ampullulse. When, there- 

 fore the ascending column is too heavy for the endosmosmic 

 force of the ampuUuloe to urge it forwards, the power of the 

 glands comes in to their assistance, and the current suffers no 

 ifiterruption in its progress. The structure of the lymphatics 

 Imprecisely the same as that of the lacteals, and the circulation 

 ^f their contents is conducted on the same principle as that 

 of the chyle. I have now to explain in what manner the 

 capillary circulation proceeds under the influence of endos- 

 mose. In the commencement of my essay, I remarked that 

 the organic solids of the body consist of minute vesicles filled 

 with a dense organic fluid, a structure resembling that of the 

 ampullulae and the glands, and therefore as favourable to 

 endosmose as theirs is. The blood which is brought to these 

 vesicles by the capillary arteries, being less dense than the 

 fluid which these vesicles contain, enters into them. As soon 

 as they are rendered turgid by this afllux, they expel their 

 contents into the capillary veins ; and these, again, convey them 

 into the larger veins, and these latter carry them forward into 

 '^fhe heart. 



^* There has been the same contrariety of opinion, respecting 

 the circulation of the sap, as has existed with regard to the 

 causes of the circulation of the blood in animals. Malpighi 

 imagined that the sap ascended, by being alternately con- 

 ' tfacted and dilated. Darwin and Willdenow ascribed the 

 '^Circulation of the sap to the contractility of the sap-vesselis, 

 "^^^d Perrault ascribed it to fermentation. Knight referred it 

 "lb the contraction and expansion of the silver grain, caused 

 "^By the change of temperature in the air ; and Hales attributed 

 Ht to capillary attraction. Dutrochet considers that the sap 

 "6f vegetables, like the blood of animals, is circulated by the 

 "J^ency of endosmose. The spongioles of the roots, which are 

 Reconstituted like the ampullulse, absorb the water which sur- 

 ^'l^Dunds them, not by capillary attraction, but by endosmosmic 

 pbwer. The spongioles being rendered turgid, by this influx 

 ^ Into them, act on the enclosed fluid, and urge it forward 

 " 'ittto the ascendinoj vessels of the stem. The leaves are com- 

 »^bsed, like the spongioles, of vesicular bodies and vessels. As 

 ^Isoon, therefore, as the lymph approaches these organs, they 

 '•draw it up towards them by endosmose. The indigested sap, 

 *" being now converted into a nutrient juice, is made to descend, 

 -by the impulsive power of the leaves, through the bark and 

 •Alburnum, by certain elongated cells called clostres. 

 "^''' It therefore seems clear that the movements of the sap and 

 "^'the circulation of the blood resemble each other in many par- 

 ticulars; and the theory which will explain the efiicient causes 



