HORTICULTURAL JOURNAL. 295 



to the condition of the tissue of the mass of which the leaves consist. But, 

 above all, the extension of the surface over which the evaporation takes 

 place during a certain time must be known, and also, the exact quantity of 

 water which is required by the root. A thick cuticle, hard like leather, 

 such as is found in succulents, Houseleek, Crassula, and Aloe, evaporates 

 little, and these plants want but little moisture. They grow often on stones 

 and rocks. On the contrary, the more tender the leaves and the thinner 

 their membranes are, the more they perspire ; and the greater the number 

 of leaves, the more liquid the stem must supply. The leaf of a Linden tree 

 has a mean size of 0.01 □ metre; the amount of both surfaces is thus, 

 0.02 □ metre; If a Linden tree has 25,000 leaves, the amount of all the 

 leaves makes a surface of 500 p metres, consequently, 2,000 trees make a 

 surface of 593 □ miles, or the extent of the kingdom of the Netherlands. 



"We readily confess, that this calculation may not be precisely correct, or 

 it may be even exaggerated. We allow, that to detrmine the number of 

 leaves can be only an approximation. Yet, we dare pretend that many a 

 tree has half a million of leaves, and that the extent of the leaves of many 

 a large well-wooded estate surpasses that of the whole Netherlands. If, 

 after these consideration, we remark how luxuriant nature is between the 

 tropics, how gigantic are the trees, how luxuriantly the plants grow under 

 those huge trees, and how elevated is the temperature, then it may be ex- 

 plained why there is an incessant dampness in those forests, on account of 

 which they are often impenetrable ; and, in what is their relation with the 

 state of the atmosphere, on account of the continual evaporation on the 

 surface. It would require a series of experiments to determine the quantity 

 of moisture evaporated by a single tree. What we can say of it now rests 

 greatly on an approximation, for the foundation of which an experiment was 

 made on another plant many years ago. If each Linden leaf evaporates 

 from June to October, during 137 days, the 5,000th part of a pound of 

 water, the mass of liquid which passes through a tree, covered with 25,000 

 leaves, is of 171J cubic metres. This approximation must be, however, far 

 beneath the truth. — Gardeners Chronicle. 



ORCHARD HOUSES. 



Mr. Rivers' Nuiisery, Sawbridgeworth. — One of the most interesting 

 features of this nursery is its orchard houses, of which there are no fewer 

 than 25. Mr. Rivers has found such contrivances so extremely useful, not 

 only for the growth of small fruit trees in pots, but also for a variety of 



