Martinengo Cesarescos Liberation of Italy (London, 1895) is to be strongly recommended, and is indeed, for accuracy, fairness and synthesis, as well as for charm of style, one of the very best books on the subject in any language; Bolton Kings History of Italian Unity (2 vols., London, 1899) is bulkier and less satisfactory, but contains a useful bibliography.
As the stele is traced farther upwards it becomes bulkier, as do the successive leaf-bundles which leave it.
It does not at first appear to be the same with the bulkier plants, such as the ordinary green herbs, shrubs or trees, but a study of their earlier development indicates that they do not at the outset differ in any way from the simple undifferentiated forms. Each commences its existence as a simple naked protoplast, in the embroyo-sac or the archegonium, as the case may be.
No doubt the primary object of the cell-wall of even the humblest protoplast is protection, and this too is the meaning of the coarser tegumentary structures of a bulkier plant.
The vesicles of Fucaceae and Laminariaceae prevent the sinking of the bulkier forms. But why certain Fucaceae favour certain zones in the littoral region, why certain epiphytes are confined to certain hosts, why Red and Brown Algae are not better represented in fresh water or Green Algae in salt, - these are problems to which it is difficult to find a ready answer.