49^ PHANEROGAMS, 



plant may be termed, in reference to the formation of its flowers, uniaxial, in the other 

 cases bi-, tri-axial, &c. "When a plant produces only terminal flowers, or when the 

 lateral flowers spring from the axils of single large foliage-leaves, they are said to be 

 solitary. When, on the other hand, the flowering branchlets are densely crowded, 

 and the leaves within this region of ramification are smaller and of a different form 

 and colour from the others, or are entirely absent, an Inflorescence arises, in the nar- 

 rower sense of the term, usually sharply differentiated from the vegetative region of 

 the plant, and not unfrequently assuming very peculiar forms which require a special 

 terminology. This occurs however only rarely among Gymnosperms, the formation 

 of multifloral inflorescences of peculiar form being characteristic of the more highly 

 developed difi'erentiation of Angiosperms ; and it will therefore be convenient to defer a 

 more detailed classification and definition of inflorescences until we are treating of 

 that class. 



With reference also to the Histology ^, one point only need be mentioned here, in 

 which Gymnosperms and Angiosperms agree. The Fibro-'vascular Bundles of Phane- 

 rogams exhibit the characteristic peculiarity that every bundle which bends outwards to 

 a leaf is only the upper limb of a bundle which runs downwards into the stem ; in other 

 words, we have here * common ' bundles, each of which has one lirhb that ascends and 

 bends out into the leaf, and another which descends and runs down into the stem ; the 

 latter is called by Hanstein the 'leaf-trace.' In the most simple cases {e.g. in most 

 Coniferse) only one bundle bends out into each leaf; but when the insertion of the leaf 

 is broad, or the leaf is large and strongly developed, a larger number of bundles pass 

 from the stem into the leaf, in which they ramify when the lamina is broad ; the leaf- 

 traces may consist therefore of one or more bundles. The bundles are usually thicker 

 at the spot where they pass from the stem into the leaf than lower down in their course. 

 Each bundle of this kind may pass downwards through only one internode or through 

 several ; in the latter case an internode with several leaves standing above it contains 

 the lower parts of bundles which bend outwards above into leaves of different height 

 and different age. The descending foliar bundle seldom has its lower extremity free ; it 

 is usually attached laterally to the middle or upper part of a lower (or older) bundle. 

 This may take place by the bundle splitting below into two branches which anastomose 

 with the lower bundles; or the thin ends of the descending bundles may intercalate 

 themselves between the upper parts of older foliar bundles ; or each bundle may bend 

 right or left and become finally joined laterally to a lower bundle. In this manner the 

 foliar bundles, originally isolated, are united laterally in the stem into a connected 

 system ; and this, when copiously developed, gives the impression of having arisen by 

 branching, whereas it arises in fact from the coalescence of separate portions originally 

 distinct. 



Besides the descending limbs of the common bundles, others may however occur in 

 the stem of Phanerogams ; first of all net-works (as in Grasses) or girdle-like reticula- 

 tions (as in Rubiaceae or Sambucus) are frequently formed in the nodes of the stem 

 by horizontal bundles. Furthermore, longitudinal bundles may become differentiated in 

 the stem, which have nothing to do with the leaves ; and the mode of formation of 

 these * cauline bundles ' may vary greatly. They originate either at an early period in 

 the primary meristem of the stem, immediately after the foliar bundles and in the pith 

 (as in Begoniaceae, Piperacese, and Gycadeae), or only at a much later period in the 

 outer layers of the stem when this has continued to increase in thickness, outside the 

 foliar bundles (as in Menispermaceae, Aloineae, and Draccena). 



The further development of the foliar bundles varies in Monocotyledons on the one 

 hand and in Gymnosperms and Dicotyledons on the other. In the former they are 

 closed ; in the latter a layer of formative cambium remains, which, in stems that increase 

 rapidly in thickness and become woody, usually prolongs itself across the medullary 



[For further details see De Bary, Vergleichende Anatomie der Phanerogamen und Fame, 1877.] 



