IRISH GARDENING 



VOLUME VIII. 



No. 86 



Edited by C- F. Ball. 



A MONTHLY JOURNAL DEVOTED TO THE 



ADVANCEMENT OF HORTICULTURE AND 



ARBORICULTURE IN IRELAND 



APRIL 

 i9Li 



Grey^leaved Rock Plants. 



Bv R. Lloyd Praegeb. 15. A. 



LIB \ 



NE\y 



A large number of the most familiar plants of 

 the rock-garden are grey-leaved. Sometimes, 

 as in some species of Helichrysum and in Diotis 

 candidissima, the term white might be used 

 instead of grey ; and from this extreme we have 

 a descending 

 series through 

 grey to greyish- 

 green, and finally 

 to green. This 

 tendency to grey- 

 ness, as seen in 

 such genera as 

 Artemisia, Achil- 

 lea, Di an thus. 

 Saxifraga, Alys- 

 sura, Arabis, and 

 so on, is the most 

 striking feature 

 in connecti on 

 with the foliage 

 of such plants, 

 and is of high im- 

 portance to us in 

 diversifying our 

 gardens when the 

 plants are out of 

 flower. If the 

 grey - leaved 

 plant be exam- 

 ined with a lens, 

 or under the 

 microscope, it will 

 be found that the grey appearance is due to one 

 of several causes — it may be a close felt or tomen- 

 tum covering the leaves and stems, as in Heli- 

 chrysum ; or a dense covering of erect hairs, as 

 in Marrubium ; or an incrustation of lime, as in 

 certain Saxifrages ; or a layer of wax, as in the 

 Pinks. These coverings serve important pur- 

 poses in the economy of the plant. Sometimes 

 their main object appears to be to assist tran- 

 spiration by warding off rain which might other- 



POTENTIIXA KlLMOBINIANA . 



A new and beautiful silvery-leaved shrub, with pale-yellow 



flowers. 



wise choke the stomata — the minute openings 

 through which plants pass out their superfluous 

 water, and breathe, and absorb carbonic acid gas 

 for the manufacture of plant-food. But more 

 often this grey covering has for its function the 



protection of the 

 leaf from intense 

 sun -heat, which 

 would cause ex- 

 cessive loss of 

 water. As we 

 pass southward 

 across Europe 

 these grey-leaved 

 plants, rare in the 

 northern Alps, 

 become frequent 

 in the southern 

 Alps, and by the 

 time the Medi- 

 terranean is 

 reached, count- 

 less plants pos- 

 sess grey felty or 

 downy leaves. 

 Indeed, in no 

 part of the world 

 are grey - leaved 

 plants so charac- 

 teristic of the 

 flora as in the Me- 

 diterranean re- 

 gion. There is 

 hardly a single natural order in that area of 

 which some members do not exhibit this char- 

 acter. Grey-leaved Composites and Labiates 

 are everywhere ; and Rock-roses, Bindweeds, 

 Scabious, Plantains, and even Grasses, all are 

 found clothed in grey. This is a protection 

 against the hot dry summer which prevails there. 

 In spite of the great difference between the 

 Mediterranean climate and our Irish one, a large 

 number of these grey-leaved species grow freely 



