In a bundle examined in the basal portion of a leaf the bulk of the xylem is found to be centrifugal in position, but internally to the protoxylem there is a group of centripetal tracheids; higher up in the petiole the xylem is mainly centripetal, the centrifugal wood being represented by a small arc of tracheids external to the protoxylem and separated from it by a few parenchymatous elements.
In the Aroid family, where in some genera the plant produces one huge, much-branched leaf each season.
Amongst indefinite forms the simplest occurs when a lateral shoot produced in the axil of a large single foliage leaf of the plant ends in a single flower, the axis of the plant elongating beyond, as in Veronica hederifolia, Vinca minor and Lysimachia nemorum.
I remember well one gaunt Nimrod who would catch up a leaf by the roadside and play a strain on it wilder and more melodious, if my memory serves me, than any hunting-horn.
Alexandrinus, in which a leaf near the end was missing, so that the great prayer (cc. lv.-Ixiv.) remained unknown.
In the third and fourth flushes only one large leaf, and after that - say during October, November and part of December - no soft leaf growth is left that can be harvested in good order.
For winter use the tops of the most useful kinds of herbs should be cut when in flower or full leaf and quite dry, and spread out in an airy but shady place so as to part slowly with the moisture they contain and at the same time retain their aromatic properties.
They are characterized by the absence of that differentiation of the body into root, stem and leaf which is so marked a feature in the higher plants, and by the simplicity of their internal structure.
And others, the midrib of the leaf ends in a tendril.
The early segmentation of the embryo differs in the several groups, but usually the first leaf or leaves, the apex of the stem and the first root are differentiated early, while a special absorbent organ (the foot) maintains for some time the physiological connexion between the sporophyte and the prothallus.