30 8 FOURTH GROUP. 



from the embryo ends with a flower ; more often it grows on or ceases to grow without 

 forming a flower, and only lateral shoots of the first or second or some higher order 

 terminate in flowers ; in the first case the plant as regards the formation of flowers 

 may be said to be monaxial, in the other cases biaxial or triaxial. If a plant 

 produces only terminal flowers, or if the lateral flowers spring from the axils of single 

 large foliage-leaves, they appear scattered and solitary. If on the other hand the 

 branches which bear the flowers are close together, and the leaves within this branch- 

 system are smaller than the rest and different in shape and colour, or altogether 

 wanting, then we have an inflorescence in the narrower meaning of the word, which is 

 generally clearly distinguished from the vegetative portion of the plant which bears it, 

 and not unfrequently assumes peculiar forms requiring a special nomenclature. The 

 latter case is rare among Gymnosperms, whereas the formation of inflorescences of pecu- 

 liar shape and with a great abundance of flowers is characteristic of the more highly 

 differentiated section of Angiosperms ; hence it seems desirable to defer a more 

 detailed account of the classification and naming of inflorescences till we reach those 

 plants. 



As regards the histology of the Phanerogams one thing only need be mentioned 

 here. In both Gymnosperms and Angiosperms the vascular bundles have the marked 

 peculiarity, that each bundle that bends outwards into a leaf is only the upper limb of 

 a bundle passing downwards in the stem ; in other words, the bundles are common 

 bundles and each has an ascending portion which bends outwards into a leaf and a 

 descending portion which traverses the stem ; the latter is called the leaf-trace-bundle, 

 after Hanstein. In the simplest cases, as in most Conifers, only one bundle bends out 

 into each leaf; but if the insertion of the leaf is broad or the leaf itself is large and 

 strongly developed, several or even many bundles may pass from the stem into the leaf, 

 where they branch if the leaf is broad ; there are therefore leaf-traces with one or with 

 more bundles. The leaf-trace-bundles' are generally thicker at the spot where they 

 pass from the stem into the leaf, that is to say at the bend, than in the lower part of 

 their course ; each leaf-trace-bundle may either run downwards through one internode 

 or through several ; an internode which has several leaves above it has in it the lower 

 portions of bundles, which bend out above into leaves of different height on the stem 

 and of different age. The descending leaf-trace-bundle is never free at its lower end, 

 but attaches itself laterally to the middle or upper part of a lower and older bundle ; it 

 sometimes happens that the bundle splits below into two limbs which anastomose with 

 the lower bundles, or the slender extremities of the bundles coming down from above 

 thrust themselves between the upper parts of the leaf-traces of older leaves, or each 

 bundle bends to the right or left and ultimately attaches itself to a lower bundle. In 

 this way the leaf-traces which were originally isolated become united in the stem into 

 a connected system, which when sufficiently developed gives the impression of having 

 been produced by branching, while it is really due to the subsequent coalescence of 

 separate portions. 



But other bundles may be formed in the stems of Phanerogams besides the leaf-trace- 

 bundles or descending limbs of the common bundles ; a net-work is often formed by 

 bundles running horizontally in the nodes of the stem, as in the Gramineae, or girdle-like 

 anastomoses also in the nodes, as in the Rubiaceae and Sambucus. Again, longitudinal 

 bundles may be differentiated in the stem which have nothing to do with the leaves, 

 and these cauline bundles may originate in different ways ; they may appear at an 

 early period in the protomeristem of the stem immediately after and inside the leaf- 

 traces in the medullary tissue, as in the Begonieae, Piperaceae, Cycadeae, or they are 

 formed much later outside the leaf-trace-bundles in the periphery of the stem as it 

 continues to grow in thickness, as in the Menispermeae and Dracaenas. 



The subsequent history of the leaf-trace-bundles of the Monocotyledons on the one 

 hand, and of the Gymnosperms and Dicotyledons on the other, is different ; in the 

 former they are closed, in the latter a layer of active cambium remains behind, which 



