140 



The Functions of the Ctimhing Roots of Ivy. By 

 Commander Norman, R.N., Fellow Bot. Soc, Edin. 



(PLATE IV.) 



I find that it always surprises the non-botanical mind, 

 and very naturally so, to learn that the solid matter of 

 plants and trees — even of the very largest, heaviest, and 

 most imposing denizen of the fcjrest — is derived from the 

 air through the leaves, and very little indeed, just a few 

 buckets of ash in the case of a moderate sized tree, from 

 the soil. 



Yet, of course, as we are all aware, there must be a soil 

 connection, or, in the case of aquatic plants, a water con- 

 nection, or those mineral constituents which are indispensable 

 to the growth, health, and identity of the plant or tree 

 cannot be obtained. 



The aerial roots of many tropical plants, including the 

 epiphytal or non-terrestial section of orchids, serve to attach 

 them to branches and other supports, and help no doubt 

 to supply them with moisture; but with what else does not 

 seem clear, as they are physiologically different from true 

 roots. In the case of ivy, however, we have a plant with 

 roots in the soil, whose branches are furnished with climbing 

 rootlets or fibrous attachments as well, which are supposed 

 to serve merely for mechanical su^iport, and not to be true 

 roots in any physiological sense. 



In my garden I have ivy upon walls and ivy upon banks, 

 and while that iu the former position is furnished with them 

 as usual, that upon the latter is wholly destitute of any 

 indication of climbing attachments ; but this is merely a 

 reminder from personal observation of a well-known habit. 



It is clear, therefore, that the climbing roots of ivy are 

 products of the necessities of the situation, and my ideas 

 have been directed to the supposition that in exceptional 

 situations to supply abnormally urgent necessities, these 

 climbing roots may be more capable than has generally been 

 supposed of performing the functions of true soil roots. 



