126 ACTION OF THE ATMOSPHERE 



Mrs. B. The saline particles are too ponderous to be 

 carried to such a height ; but there you experience the 

 salubrious effect of mountain air. The salt is not requi- 

 site to render it tonic : it is only when you descend on 

 the opposite side into the inland country, that you per- 

 ceive the want of those invigorating qualities for which 

 the sea-air is so celebrated. 



It is remarkable that kelpwort exudes a portion of the 

 alkali which it receives from the atmosphere into the 

 ground, the soil on which it has been cultivated being 

 found to contain more than when such a crop has not 

 been raised upon it. This is owing, probably, to the 

 quantity it absorbs, being more than the plant requires. 



Emily. This, then, affords an exception to the gene- 

 ral nature of the exudation of plants by the roots, as it 

 must constitute appropriate nourishment for other plants 

 of the same species. 



Caroline. And is not the air also useful as a vehicle 

 to transport small seeds from one country to another ? 



Mrs. B. Yes ; there is scarcely any resemblance be- 

 tween the plants of Europe and of America, excepting 

 in Cryptogamous plants, because the seeds of lichens, of 

 mosses, and of fungi, of which this family is composed, 

 are so small that they float in the air, and are transport- 

 ed by the wind from one continent to the other. 



The wind also performs the part of a careful sower, 

 dispersing the seeds which fall from the plant with regu- 

 larity over the soil. 



Caroline. I wish it would distinguish between weeds 

 and flowers > and confine itself to the dispersion of useful 

 seeds ; but it seems to delight in the propagation of 

 weeds : if any thistles or groundsel are to be found in a 

 garden, the wind is sure to carry the seeds all over it. 



Mrs. B. The distinction between weed and flower is 

 not so easily made as you may imagine. In botany we 

 know not what weeds are ; every plant has its use for 

 some purpose or other. 



702. In evaporation of the sea water why do not the saline particles 

 rise highl 703. Is salt needed in these evaporations as a tonic'? 

 704. In kelpwort what is mentioned as being remarkable"? 705. To 

 what is this owingl 706. What plants are common to Europe and 

 America 1 ? 707. Why are these common ta the two. countries! 

 708. What is said of weeds and plants* 



