466 PHA NER GA MS. 



mentioned at p. 72 (Fig. 60). The middle layer of the tissue of the leaf, in which also 

 the fibro-vascular bundles run, has usually a peculiar development in Gymnosperms ; in 

 Cycadeae and Podocarpeae it consists of cells elongated in a direction transverse to the 

 axis of the leaf and to the bundles, but parallel to the surface of the leaf, leaving large 

 intercellular spaces (Transfusion-Tissue of Mohl), In the acicular leaves of the 

 Abietineae the fibro-vascular bundle, split into two, is enveloped by a colourless tissue, 

 which is sharply differentiated from the surrounding chlorophyll-tissue (Fig. 89, gby 

 p. 105). It is parenchymatous, and is distinguished by the large number of peculiar 

 pit-like markings (Fig. 326) ^ 



A NG I OS PERM SI 



Monocotyledons and Dicotyledons are distinguished from Gymnosperms by 

 the following characters : — their ovules are form.ed within a receptacle, the Ovary ; 

 the endosperm originates in the embryo-sac only after fertilisation, the pollen-grain 

 emits its pollen-tube as an outgrowth of its inner cell-wall (intine) without any 

 previous internal cell-formation ; — characteristics, the immense importance of which 

 has already been shown in the general introduction to Phanerogams. Concurrent 

 with these distinctions there are however a number of other peculiarities in these 

 plants taken as a whole which distinguish them from all other vascular plants ; and 

 this is especially the case with the structure of the flowers and the fruit, the 

 normal morphological characters undergoing such peculiar combinations and changes 

 that a more detailed description of them must precede the special description of the 

 two classes which they include. 



The Floiver as a ivhole^. The flower of Angiosperms is rarely terminal, /. e. 

 the primary stem, which is a prolongation of the axis of the embryo, rarely termi- 

 nates in a flower, making the plant uniaxial. When this is the case a sympodial 

 or cymose inflorescence is usually developed, new axes with terminal flowers 

 arising beneath the first flower ; but it is more common for only axes of the 

 second, third, or a higher order to terminate in a flower, so that the plant may 

 in this respect be termed bi-, tri-, or multi-axial. 



While in Gymnosperms the flowers are typically unisexual or diclinous, herma- 

 phroditism largely prevails among Angiosperms, although monoecious and dioecious 

 species, genera, and famihes are not uncommon. The male flowers are sometimes 

 essentially different in structure from the female flowers (as in Cupuliferae and 

 Cannabinese), but in most cases the unisexuaHty arises merely from the partial or 



' For further details, see Mohl, Bot. Zeit. 1871, Nos. 1,2. 

 ^ From ar^^uov^ a receptacle, capsule, ovaiy, and crirtpfia, seed. 



^ The most important and comprehensive work on the flowers of Angiosperms is Payer's Traite 

 d'Organog('nic de la Fleur (Paris 1857) with 154 plates. 



