Dlst and its Importance to Plant Life. lo 



of their foousalts from the atmosphere. Yet there is plenty of 

 evidence to show that the leaves not only can but do absorb both 

 water and any salts that may be dissolved in it. 



The experiments of De Saussure, of Boussingault, and of 

 Henslow seem to be conclusive on this point.* Few would have 

 the audacity to question such high authority as that of both Sachs 

 and Pfeffer, who both admit that such absorption can take place. 

 I think, therefore, that I am justified in assuming that both water 

 and dissolved salts can be directly taken up by the foliage. 



Mr Jamieson, of the Agricultural Research Association 

 (Aberdeen), has suggested that certain hairs upon the leaf are able 

 to assimilate the gas nitrogen. t For so startling a theory as this 

 Mr Jamieson 's experiments seem to me insutificient, and in any 

 case they would have to be confirmed by other observers before 

 (jrdinary botanists can be expected to agree with him. 



Amongst the dust collected on the leaves certain small 

 animals are often to be seen. There are the mites or acarids, 

 which are exceedingly common and obtrude themselves upon one's 

 notice. They run actively about the veins and petioles, especially 

 in dark or cloudy weather, but in bright sunshine seem to retire to 

 rest, either in special shelters or in any convenient crevice about 

 liie leaf or stem. There are many kinds of mites, of which s<nne, 

 such as Red Spider (Tetranychus, Bryobia, Tenuipalpus) and 

 Rhizoglyphus (Bulb mite), are exceedingly dangerous pests, whilst 

 others live parasitically on animals or on decaying organic matter 

 (cheese mite).| But these particular mites appear to be quite 

 harmless or, more probably, are distinctly benevolent in character. 

 They are said, in the first place, to devour the spores of fungi as 

 well as insects' eggs, and so prevent the leaves from being infected 

 liy dangerous parasites. § Thus, in Brazil, where many plants are 

 seriously injured by various algae, lichens, and fungi, which grow 

 upon their leaves, it is stated that those shrubs and trees which 



* Sacl).s, PfefFei-, Heiivslow. 



t Jamieson. 



+ Tetranychus telarius var russeolus can live upon man as well as 

 upon plants. It passes the winter on bark, but spends 4-7 

 months on the leaves. In Italy people living near plane trees 

 have suffered from irritation of eyes, nose, and throat, which 

 is due to this insect, probably carried with the hairs and dust 

 from the trees. 



§ Lundstrom, Delpino. 



