I would venture, then, to suggest these considerations as throwing light on the reason why herbaceous plants so often have their leaves much cut up.[1]
Next let me say a few words on the reasons why some plants have broad and some narrow leaves. Both are often found within the limits of a single genus. I have ventured to indicate the distance between the buds as a possible reason in certain cases. It would not, however, apply to herbaceous genera such as Plantago or Drosera. Now, Drosera rotundifolia (Fig. 25) has the leaves nearly orbicular,
| Fig. 25. | Fig. 26. |
while in D. anglica (Fig. 26) they are long and narrow. Plantago media (Fig. 27) has ovate leaves, while in P. lanceolata (Fig. 28) they are lanceolate, and in P. maritima nearly linear. More or less similar cases occur in Ranunculus.
These differences depend, I believe, on the attitude of the leaf, for it will be found that the broad-leaved ones are horizontal, forming a rosette more or less like that of a daisy, while the species with narrower leaves carry them more or less erect. In the daisy the rosette lies on the ground, but in other cases, as in Daphne (Fig. 29), it is at the end of a branch.
Any one who has looked with an observant eye at the vegetation of hot, dry countries must have noticed how much the general character of the vegetation differs from that which prevails in a climate like ours. There is a marked increase of prickly, leathery, and aromatic species. The first two characteristics evidently tend to protect the leaves. As regards the third, Mr. Taylor,[2] in his charming book on
- ↑ Mr. Grant Allen, who had been also struck by the fact that herbaceous plants so often have their leaves much cut up, has suggested a different explanation, and thinks it is due to "the fierce competition that goes on for the carbon of the air between the small matted undergrowth of every thicket and hedge-row."
- ↑ Page 311.
