70 ON SAP. 



f 



Caroline. This seems to me to comprise the whole 

 history of vegetation. 



Mrs. B. In a general point of view it does, but we 

 shall yet have many details to enter into ; besides, what I 

 have hitherto said relates only to the nourishment of 

 plants : their re-production is of no less importance, and 

 we have not yet ever alluded to the flower, the most dis- 

 tinguished and beautiful of their organs, and that in which 

 the seed originates. 



Emily. But this sap, Mrs. B., which I imagined to be 

 diffused through the plant as it rose, seems to be dispos- 

 ed of in a very different manner: part you say is exhaled 

 by the leaves ; and part descends through the bark ; what 

 then remains to nourish the plant ? 



Mrs. B. All that is necessary for that purpose is se- 

 lected and retained. If you consider that the sap which 

 rises in the roots consists simply of water, holding in so- 

 lution a variety of crude ingredients, such as lime, silex, 

 magnesia, soda, and potash, you will acknowledge that 

 something more is required than the mere diffusion of this 

 heterogeneous fluid through the plant in order to nourish 

 it. The sap traverses the stem, rising, as I have already 

 said, through the alburnum, and some small portion of it 

 through the perfect wood. A great variety of experiments 

 have been made, with a view of ascertaining the degree 

 of rapidity with which the sap ascends. M. Bonnet rais- 

 ed some plants in a dark cellar, in order to blanch their 

 stems, that he might be able to trace the ascent of the co- 

 lored water with which he nourished them. He found 

 that this tinted sap rose only four inches in two hours ; but 

 the plants, owing to the disadvantageous circumstances 

 under which they were cultivated, were weak and sickly ; 

 in subsequent experiments on more healthy plants, the 

 sap was seen to ascend three inches in the course of an 

 hour. Some time afterwards Mr. Hales immersed a fresh 

 cut branch of a vigorous pear-tree in a tube full of water, 

 and found that the sap rose in it eight inches in six min- 

 utes. 



877. What is here said of the re-production and flowers of plants! 

 378. What crude ingredients must the sap be considered as holding in 

 solution! 379. What experiments were made by Bonnet! 380. 

 What ones were made by Mr. Hales! 



