Respiration. 561 
the greatest care has been exercised in the removal to secure 
all the roots without injury, and when abundance of water is 
within their reach. This may arise from a paucity of small 
roots ; and when a tree has but a few large coarse roots, it is 
almost impossible to lift it with a ball of earth ; and a very short 
exposure of the fibrils to a drying wind will destroy their delicate 
spongioles or absorbing parts. Some plants will readily replace 
their fibrils, whilst others, and especially those with coarse roots, 
do so with difficulty, or not at all, if the circumstances be un- 
favourable. In instances of this kind it is useless to confine 
one’s attentions to the roots. The top must be cared for, and 
this is best done by covering it over with bast mats in very hot 
sunny or drying weather. From time to time the mats should 
be moistened to moderate the transpiration of the plant. The 
trouble involved in this operation would be amply repaid by 
the preservation of choice shrubs. 
After a prolonged drought the leaves of many herbaceous 
plants, whose roots do not penetrate far into the soil, droop 
during the day when exposed to the fierce rays of the sun, 
because the evaporation is in excess of the absorption. But 
the dews of night are sufficient, as a rule, in our climate, to 
afford them moisture enough to rise again and recover their 
former firmness. In hotter, drier climates, however, as in 
some parts of tropical and sub-tropical Africa, a great number 
of plants succumb, that would otherwise have enjoyed a much 
longer existence. In dull, rainy weather the amount of evapo- 
ration is almost nil. 
From the differences in their structure, plants possess greater 
or less power of resisting the effects of continued dry weather. 
These differences are in texture, number of stomates, thickness 
of epidermis, and also depth reached by the roots. Relatively, 
annual and perennial herbs suffer more from drought than 
woody and arborescent plants; and aquatic plaints wither 
almost directly they are taken from the water. Trees with 
coriaceous leaves, like the common Box, with hard wood or 
deep roots, suffer little from long droughts; and the same. 
may be said of most plants with succulent, fleshy leaves or 
stems, owing to their thick epidermis and few stomates. The 
plants belonging to the latter category abound in hot, dry 
countries. 
The condensation of the sap in the tissues of the leaves is 
insufficient of itself to give it the necessary nutritive pro- 
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