Organography of plants, especially of the archegoniatae and spermaphyta . the course ofthe nerves. Fraxinus excelsior. Fraxinus gives us an example of a pinnate leaf (Fig. 224). The pinnules arelaid down in acropetal suc-cession, and there appearsin the broad base of the leaf-primordium a large num-ber of conducting bundles(Fig. 224, C), which radiatefrom one another in corre-spondence with the growthof the pinnules. As thepinnules separate from oneanother at a later period,there is formed from a por-tion of the upper leaf be-tween each pair a stalk-likeleaf-spindle or rhachis, andthe original
Organography of plants, especially of the archegoniatae and spermaphyta . the course ofthe nerves. Fraxinus excelsior. Fraxinus gives us an example of a pinnate leaf (Fig. 224). The pinnules arelaid down in acropetal suc-cession, and there appearsin the broad base of the leaf-primordium a large num-ber of conducting bundles(Fig. 224, C), which radiatefrom one another in corre-spondence with the growthof the pinnules. As thepinnules separate from oneanother at a later period,there is formed from a por-tion of the upper leaf be-tween each pair a stalk-likeleaf-spindle or rhachis, andthe original arrangement ofthe bundles is lost. Theleaf-stalk here exhibits alsoa growth in thickness, andthe bundles are arrangednearly in a circle. Amongst the Dicotyle-dones there are also caseswhere the leaf-stalk is dis-tinguished from the laminaonly by its small size. Itarises then relatively lateand has the vascular bundles arranged in one row, as, for example, inPlantago media, whose leaf-lamina has the primary veins arranged quitelike that of the type of Fig. 224. Fraxinus excelsior. A, tip of the shoot from the out-side. Right and left of the apex the primordia of pinnate leavesalready show the acropetal pinnules. B, bud in transverse , initial strand in base of young leaves; f, vascular bundle inbasal part of leaf-stalk of next older leaf; c\ vascular bundle inupper part of leaf-stalk. C, young leaf showing the pinnules a, c, d,and the conducting bundles /, 7/, ///. /?, scheme of the course ofthe conducting bundles in the adult leaf, lettering as in C. AfterDeinega. ADAPTATIONS OF THE LEAF 345 mM^ V CONNEXION BETWEEN CONFIGURATION OF LEAF ANDRELATIONSHIPS OF LIFE. HETEROPHYLLY Frequent reference has been made to the connexion between configura-tion of leaves and the relationships of life, and a comprehensive treatmentof this subject is scarcely possible without a pretty full account of anatomicalstructure, and this is beyond the scheme of this book. We
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