THE GROWTH OF THE SHOOT FROM THE BUD 51 



epidermis of the stem. These cells closely resemble those of the 

 leaf, they are full of chlorophyll grains, and carry on the work of 

 carbon assimilation. The Marsh Samphire or Glass wort has no 

 leaves, whilst Saltwort has very much reduced leaves. 



(ii.) TRANSPIRATION. Leaves are not only engaged in carbon 

 assimilation, but also in transpiration. Land plants that live in 

 the medium of our atmosphere are constantly having water pulled 

 from them by the atmosphere. This is made good by the power 

 of absorbing water which the roots possess, as already described 

 in the last chapter. This water passes off into the atmosphere 

 from the surface of the leaf. Every one knows by experience that 

 one of the first signs of withering in a plant is the drooping of the 

 leaf ; watering the roots, if done in time, allows the plant to 

 recover. 



One of the simplest experiments, showing that water passes 

 off from the leaf surface is to put some ivy leaves with their long 

 stalks through a piece of cardboard into a tumbler full of water ; 

 on the top of the cardboard place a dry tumbler of the same size 

 over the blades of the leaf. In a few hours, drops of water will 

 collect on the sides of the tumbler and the water in the lower 

 tumbler will gradually lessen. This is always happening in a 

 dry atmosphere. When the air is laden with moisture, the leaves 

 give off little, if any, water. Yet it is in dry situations that it is 

 important for the plant to retain as much water as possible. The 

 leaf has various contrivances for securing this. It may have a 

 very thick skin, as in the Holly ; it may be very hairy, as in the 

 Hawkweed, Crepis, and many other Composites growing on hills, 

 or it may curl up so as to shelter the stomata (see Fig. 28) com- 

 pletely, and thus prevent the giving off of water from its surface. 

 There is a certain relation between the shape of leaves and the 

 dryness of the situation. The Conifers are characteristic of dry 

 soils ; their leaves are very much reduced and acicular in form ; 

 the Heaths, the Acacias of Australia, the Gorse, the Cacti are 

 instances of plants belonging to dry situations and having very 

 much reduced and often spiny leaves. 



Plants living submerged in water hardly transpire at all, and 

 do not have water conducted through them, as in land plants. 



