

DIV. I MORPHOLOGY 123 



examined the branch is placed with its subtending leaf towards the 

 observer (ANTERIOR), and the parent axis POSTERIOR (Fig. 144 A), 

 and so that the median plane of the subtending leaf coincides with 

 that of the observer. Structures on the lateral branch, which are 

 directed towards its subtending leaf, are termed anterior, those 

 towards the parent shoot posterior, while right and left refer to 

 structures lying to either side of the median plane of the subtending 

 leaf in the TRANSVERSE PLANE. 



Independently of the phyllotaxis, the lowest leaves of a lateral 

 bud which come next above the subtending leaf tend to occupy a 

 definite position in relation to the latter and to the parent axis. 

 They connect the phyllotaxy of the lateral branch with that of the main 

 shoot. In Monocotyledons there is one such BRACTEOLE (Fig. 144 vb), 

 while in Dicotyledons there are two bracteoles ; they are usually scale 

 or bracteal leaves. The bracteole in Monocotyledons is median and 

 stands on the posterior side of the branch towards the main axis. It 

 frequently has two lateral veins appearing as keels, while a middle 

 vein is wanting (Fig. 144 A)\ it may thus be regarded as arising 

 from the union of two lateral bracteoles C 38 ). In Dicotyledons the two 

 bracteoles (a and /5) stand as a rule right and left in the transverse 

 plane, the later leaves following in a different arrangement. 



Apart from this the lateral buds may show the same leaf arrange- 

 ment as the parent axis or may differ from this. 



When the phyllotaxy is spiral the genetic spiral of the branch may either run 

 in the same direction as that of the main axis (homodromous) or in the opposite 

 direction (antidromous). 



(c) Construction of the Branch System. The general aspect or 

 habit of every shoot-system depends, in addition to the direction of 

 growth of its main axis, on the following features : the number of 

 orders of lateral axes that develop; the position on the main axis 

 of the buds which grow out as lateral branches ; the intensity of the 

 growth and the orientation of the lateral axes of various orders in 

 relation to one another and to the parent axis. The variety in the 

 general habit of the shoot-systems frequently also stands in relation 

 to the mode of life of the plants. 



1. DIRECTION OF GROWTH OF THE MAIN Axis OF THE SHOOT- 

 SYSTEM. This, in the first place, determines the general type of the 

 shoot-system. 



If the main axis stands at right angles to the soil, the shoot is termed 

 ORTHOTEOPOUS and the plant erect. In this case the more or less plagiotropous 

 and dorsi ventral lateral branches tend to be distributed radially when the plant is 

 growing freely. If the main axis is growing obliquely or horizontally, and is thus 

 PLAGIOTROPOUS, the arrangement of the branches is usually dorsiventral ; when 

 such a main axis with its lateral branches remains on the surface of the soil or 

 grows horizontally beneath this, the plant is CREEPING. The lateral branches tend 



