ANGIOSPERMS. 599 



part of which — the leaf, — or the other part — the branch, — may be developed earlier 

 than the other or simultaneously with it, or more or less completely than it. It is 

 evident in the vegetative region that the subtending leaf always arises first, and de- 

 velopes more actively, to begin M'ith at any rate, than the corresponding branch which 

 only becomes apparent when one or more young leaves have arisen above the leaf 

 in question. (Figs. 129, 131.) In many inflorescences the development of the leaf 

 precedes that of the axillary branch by a much shorter interval, as in the spikes and 

 racemes of Amorpha^ Salix, Rudbeckia, Lupinus, Veronica, Digitalis, Orchis, Delphinium. 

 In the development of other inflorescences the axillary branches are formed immediately 

 after their subtending leaves, so that no rudimentary leaf intervenes between the apex 

 of the shoot and the youngest axillary branch {Plantago, Orchis, Epipactis). Sometimes 

 leaf and branch arise simultaneously, as in the Gramineae, Cytisus, TrifoHum, Orchis, 

 Plajitagc, Ribes. Or again, the axillary branch is formed first, before its subtending 

 leaf, in which case the leaf attains only a slight development, its presence being merely 

 indicated as in Sisymbrium, Brassica and other Cruciferae, Umbelliferae, Anthemis, 

 Valeriana, Asclepiadeae, Bryonia, Cucumis. Or the subtending leaf may not make its 

 appearance at all, and no bracts are developed, as in many Cruciferae (Fig. 132), 

 Gompositae, Gramineae, Umbelliferae, Papilionaceae, Gucurbitaceae, Asperifolieae, Solaneae, 

 Hydrophylleae, Saxifrageae, Potamogetoneae. In all these inflorescences the youngest 

 buds are nearer to the apex of the parent shoot than any foliar organs in so far as these 

 have been developed, but the branching must not on this account be regarded as 

 dichotomous. A dichotomy of the parent shoot only takes place when a vigorous 

 branch is developed so near to the apex that a continuation of the direction of growth of 

 the shoot is rendered impossible, its apex apparently dividing into two or more apices. 

 According to Warming this is the case in Hydrocharis, Vallisneria, the Asclepiadeae, the 

 scorpioid cymes of the Solaneae, Asperifolieae, Hydrophylleae, Gistaceae, and many 

 Gucurbitaceae. This tendency to dichotomise shown by plants the vegetative parts of 

 which branch in a lateral axillary manner is doubtless connected with the suppression 

 of the development of leaves in the inflorescences, and this is confirmed by the fact that 

 the tendrils of Vitis and Cucurbita, on which the development of leaves is rudimentary, 

 exhibit the same tendency. ^ 



The axillary branches of the vegetative region are usually so placed that they arise 

 both from the basis of the leaf and from the tissue of the stem ; but it sometimes 

 happens that the branch is entirely transferred to the stem and becomes isolated from the 

 leaf. In the floral region, on the other hand, it not unfrequently happens that the axillary 

 branch (the inflorescence) arises solely from the leaf, as in Hippuris (Fig. 119), Amorpha, 

 Salix nigricans. If, however, the subtending leaf (bract) is developed later than the axil- 

 lary branch (inflorescence), it may arise from it, so that the leaf has no direct connection 

 with the parent shoot, but appears to be the first lowest leaf of the lateral branch ; this 

 is the case, according to Warming, in Anthemis, Sisymbrium, Umbelliferae, and to a slight 

 degree in Papilionaceae, Orchideae, Valerianeae, and others. These relations are usually 

 evident at the earliest stage of development, but frequently the subtending leaf is found 

 upon the axillary branch in the mature condition, as in Thesium ebracteatum, Samolus 

 Valerandi, Boragineae, Solaneae, Grassulaceae, Spiroea, Loranthaceae, Ipomcea bona nox, 

 Agtt've americana, Ruta, Paliurus, Tilia (in which this applies to the large bract of the 

 inflorescence), and others. 



3. Number and Relative Position of the Parts of the Floiver'^. Just as the forms of 

 branching of the inflorescence are usually diff"erent from those of the vegetative stem, 

 the arrangement of the leaves of Angiosperms is also usually diff'erent on the shoot which 

 constitutes the flower from that on other parts of the same plant. The cessation of 

 the apical growth of the receptacle, its great increase in breadth, or even hollowing out, 

 before and during the time when the perianth and the sexual organs are being formed, 



[See Eichler,' BlUthendiagramme.] 



