THE LIFE -HISTORY OF PLANTS. 



97 



under all conditions in equal amount. A jobbing 

 gardener will soak a Primrose, whose sere and 

 yellow leaves and "knotting" bud ought to show 

 him that nothing is required but to let the plant 

 alone for a season ; he will pass over with a scanty 

 modicum a plant whose rapidly-growing shoots and 

 expanding foliage should be enough to proclaim the 

 necessity for abundant supplies. 



To water plants properly, demands not only obser- 

 vation but intelHgent judgment. The circumstances 

 to be taken into account are, among others, the con- 

 dition of the atmosphere as to heat and light, the 

 nature of the soil as to drainage and moisture, the 

 texture of the plant, the thickness or tenuity of 

 its leaves, the nature of its covering, thin and ex- 

 posed, leathery, or coated with hairs or waxy exuda- 

 tion ; the condition of the roots, whether they are 

 near the surface, or at a considerable depth below it, 

 whether there is an abundance of fine fibrous feed- 

 ing-roots or whether there are comparatively few, 

 whether the root or other part of the plant has or has 

 not a store of liquid to draw upon in case of need, 

 and so forth. 



Again, plants in rapid growth necessarily make 

 greater demands on their food-supplies than thej^ 

 do when at^rest ; hence, while it may be good prac- 

 tice to give plenty of water duiing the growing 

 period, it is almost always advisable to lessen the 

 amount during the flowering season ; and although 

 more water may again be required when the 

 fruit is ripening, little or none is requisite for 

 the proper maturation of the seed. Newly trans- 

 planted trees or shubs require very cautious watering 

 according to circumstances. On the one hand, they 

 must never be allowed to become dry ; but on the 

 other hand, they may suffer from supplies in excess 

 of what, in their relatively enfeebled condition, they 

 can properly digest or rid themselves of. The 

 general conditions of temperature and light with 

 reference to the amount and frequency of watering 

 need only to be mentioned, for the importance of a 

 due consideration of these factors must be obvious to 

 every one. One pitfall, however, may be pointed 

 out with a view of preventing the inexperienced 

 cultivator from being misled by climatic or geogra- 

 phical facts. A plant, let us say a native of the 

 Khasya hills, grows in a country where from 500 to 

 600 inches of rain fall annually, and as one inch of 

 rain means rather more than one hundred tons of 

 water per acre, it is quite clear that it would be im- 

 practicable to give it anything like that amount in 

 cultivation here. What we wish to show is, that it 

 would not only not be necessary for us, even if it 

 were practicable, to give such enormous supplies of 

 water, but that it would certainly be injurious to do 

 80, because we could not maintain the concomitant 

 31 



temperature and other atmospheric conditions. On 

 the other hand, although our own climate, especially 

 that of our glass-houses, is vastly more moisture- 

 laden than that of the so-called rainless districts of 

 Arabia, Scinde, or Peru, yet that circumstance need 

 not deter the intelligent gardener from undertaking 

 the cultivation of what plants may reach him from 

 those localities. 



While, therefore, geographical and especially 

 climatic indications are very valuable to the gar- 

 dener, they are of less importance for him than the 

 indications furnished by the construction and ajj- 

 pearance of the plant itself. Up to this time the 

 indications of the microscope have not been much 

 employed in the service of the gardener, nevertheless 

 it is certain that they would in many cases afford 

 essential aid to the cultivator, by revealing the 

 natural requirements of the plant as manifested by 

 its internal structure, a point that we shall have 

 to consider later on when discussing leaf-action. 

 Sufiice it here to allude to the more obvious external 

 characteristics. The smaller and finer the root-fibres, 

 the thinner the texture of the leaves and their 

 covering, the smaller the size and proportion of the 

 reserve organs, the more water is likely to be required. 

 On the contrary, where the reserve organs are largely 

 developed, as in a Cactus-stem, a bulb, or the pseudo- 

 bulb of an Orchid, where the leaves are thick and 

 juicy, or covered with a leathery rind, or one covered 

 with wax, or a thick felting of hair, there the 

 amount of water required will be relatively less, 

 except it may be for a short period when growth is 

 going on actively. It will be seen that it is not 

 only the quantity of water to be given which de- 

 mands attention, but the frequency of the dose and 

 the time when it should be administered. The 

 structural hints above given bring this out very 

 clearly, and show why it is that some plants wiU 

 flag directly if their supplies be cut off, while others 

 as clearly show that they need water only at 

 relatively long intervals, the supplies stored up in 

 their tissues being sufficient for the support of life 

 till some extra demand arises which must be met by 

 supplies from without. 



The Solid Constituents of Plants.— Water, 

 however, is not the only substance which plants 

 derive from the soil. Although it may be true that 

 eight or nine-tenths of a plant consist of water, ytt 

 the remaining one or two-tenths of solid matter have 

 to be accounted for. They enter the plant through 

 the roots and through the leaves, from the soil and 

 from the air, not indeed as solids, but either as 

 liquids or as gases. One of the main duties of the 

 plant, then, is the conversion of Hquid and gaseous 

 matter to solid substances. Of the solid substances 



