132 



FLORA AND SYLVA. 



How Stones 

 Irrigate. 



What the divine artist has lavished 

 upon the world in Nature man is enabled 

 (with certain limita- 

 tions) to reproduce. 

 Bare hard walls can be 

 clothed with life, colour, and sweetness, 

 if we have but the wit and the patience 

 to use the right materials. It is enough 

 if the wall be sufficiently deep to retain 

 moisture, and porous to allow of the 

 spread of roots. To understand the part 

 played by the stones in these conditions 

 it must be explained that all stone, 

 whether soft or hard, is porous, absorb- 

 ing moisture by capillary attraction. A 

 rock drinks up moisture as will a sponge 

 or a lump of sugar, until in wet or misty 

 weather its exposed parts become com- 

 pletely saturated. The more porous the 

 stone, the more speedy the process of 

 absorption. Stones also contain a greater 

 or less number of fissures which mine- 

 ralogists call veins. These are widened 

 by the gradual action of frost and thaw 

 into the heart of the hardest stones, and 

 by their work as channels leading water 

 into the inner cells of the rock their 

 wearing action is great. These channels 

 are more numerous in limestone than in 

 granitic rocks, and this explains why 

 the plant-life of such regions is more 

 rich and varied than upon granite for- 

 mations. Rocks thus saturated with 

 water are cool reservoirs of moisture 

 which Nature uses for irrigation. How 

 often water may be seen gushing in 

 abundance from the foot of the most 

 desolate and arid of mountains, even 

 though devoid of vegetation, and, in the 

 same way, what are to all appearance 

 the most unpromising of rocks often 



show the most dainty and brilliant flora. 

 Roots strike deep into a pile of loosened 

 fragments, or follow the deepest of fis- 

 sures into the heart of the stone itself, 

 in search of the nourishment hidden 

 there, which is drawn upon for the up- 

 building of the leaves and flowers ex- 

 posed to the outer air. From the sur- 

 face of the stone itself also there is given 

 off a constant vapour which, as a pro- 

 tecting veil, envelopes the tender leaves 

 and delicate petals, shielding them from 

 the ardent rays of the sun. It is this in- 

 fluence which enables the fern to unfold 

 its delicate fronds unhurt, though the 

 full heat of themid-day sun scorches the 

 surface of the rock. But for this natu- 

 ral protection the life of many plants 

 would be endangered by the dryness of 

 the summer atmosphere. The rock's 

 part in Nature is, therefore, to act as a 

 sponge, at one time absorbing the ex- 

 cess of moisture in the air in order to 

 render it again through the agency of 

 rock-plants, whenever a dry atmosphere 

 makes the need felt. This explains 

 the continued existence of many plants 

 which would otherwise perish under 

 the sun's rays. Wall gardens have, there- 

 fore, a great interest for all lovers of 

 plant-life, for not only are they pictu- 

 resque and pleasant to the eye, but they 

 are the means of preserving to us a 

 multitude of fragile mountain plants 

 which would otherwise die of drought, 

 from stagnant moisture, or from the 

 improper exposure and development of 

 their leaves and flowers. When so draped 

 with flowers bare walls may become gar- 

 dens full of pictures of rich beauty, ever 

 changing in their charm and variety, 



