336 FORM AND POSITION OF THE TRANSPIRING LEAVES AND BRANCHES. 



dron, Melaleuca, Protea, Banksia, and Grevillea, the leaf -blades themselves are not 

 placed horizontally like those of our maples, elms, beeches, and oaks, but vertically 

 on edge, like the phylloclades and phyllodes. Imagine now an entire wood of such 

 eucalypti and acacias, on which the mid-day sun is pouring down its rays. If it is 

 not exactly literally true to say that each vertical leaf only casts a linear shadow at 

 noon, it is at least certain that there is not much shade on the ground of such a 

 wood. The sunbeams find their way everywhere between the erect leaf-blades, 

 penetrating the depths below, and it is impossible to speak of the dim forest-light 

 under such circumstances. The Casuarinese, which grow with eucalyptus, acacias, 

 and Proteaceae do not help to make such woods shady, and thus one is quite 

 justified in speaking of the shadowless forests of Australia. 



Although Australia stands alone in the variety and abundance of its plants 

 possessing vertical leaf -blades, other floral areas furnish numerous and remarkable 

 examples of this arrangement. One has only to think of the curious shape of the 

 so-called "equitant" leaves belonging to many plants of the Lily family 

 (Tojieldia, Nartheciuni), numerous Iride83, and the closely-related genera. Gladiolus, 

 Ferraria, Witsenia, Montbretia, &c., chiefly natives of the Cape. The leaves 

 exhibit the peculiarity of being folded together lengthwise, and the sides thus 

 brought into contact become fused with one another. Only at the point where they 

 join the stem do the two halves remain distinct, forming a groove in which is 

 inserted the base of an upper leaf. The formation of such equitant leaves from 

 ordinary leaf -blades may perhaps be illustrated by taking a strip of paper smeared 

 on one side with paste and folding it longitudinally so that the pasted sides are in 

 contact and become joined together. Such equitant leaves are so directed that their 

 broad surfaces are much less exposed to the perpendicular rays of the mid-day than 

 to those of the rising and setting sun. 



In the Mediterranean flora, and on many steppes, plants are not seldom to be 

 met with whose leaves look as if they had not been able to free themselves from 

 the stem. In such plants the projecting portion of the foliage-leaf is very small, 

 but the margins are continued for some way down the stem as projecting strips 

 and wings. Leaves of this kind are termed "decurrent". They are particularly 

 abundant amongst Composites, viz. in the genera Centaurea, Inula, Helichrysum; 

 but they also occur in many Papilionaceous plants and Labiates. The position of 

 these vertical wings, which traverse the stem, is exactly the same, with regard to 

 the sun, as that of the phyllodes, phylloclades, and equitant leaves, and they behave 

 in respect to transpiration in exactly the same way. 



In many plants the blades of the foliage-leaves when young have not a vertical 

 position^ but gradually assume it during development, i.e the blades at first arc 

 turned so that the flattened surfaces are horizontal and face upwards and downwards. 

 Later they twist round at the point where they are inserted on the stem, so that 

 their margins become directed upwards and downwards. As already stated, this 

 peculiarity is observed in many eucalypti and various other Australian trees 

 and shrubs. But plants in sunny situations in other regions also exhibit this 



