298 



OM THE CAULOTAXIS OF BRITISH GERANIUMS. 



peduncle is likewise a lateral branch, developed in the axil of a 

 leaf, but having from the first a more vigorous growth than its 

 fellow on the opposite side, and much more than the parent axis 

 from which it springs. This branch, besides growing more 

 vigorously than the other, sets itself more or less closely in a line 

 with the internode below, and as a consequence becomes part of the 

 pseud-axis of the plant, and the parent axis, with the flowers, is 

 pushed into a lateral j)osition. 



Incorporating this view^ of the caulotaxis with the features of it 

 already described, we may reconstruct the shoot diagrammatically, 

 as in Fig. 2. Thus the lowest part of the central axis [a] bears at 

 the first node two leaves, and then runs out into an apparently 

 lateral peduncle (d). In the axils of the leaves lateral branches 

 are j)roduced in a normal fashion, but there is a marked difference 

 between them. One [h] remains permanently in the condition and 

 with the appearance of a subordinate branch ; but the other (c) 

 outgrows this both in length and stoutness, and, setting itself in a 

 line with the internode below, pushes its parent axis ((/) over into 

 a lateral position, as already stated. 



The other nodes and internodes having a similar organisation 

 and origin, it seems clear that what appears to be the main axis 

 of a shoot of this plant is merely a pseud-axis, formed from the 

 lower portions of successively developed lateral axes. But there is 

 a difficulty in classifying this form of caulotaxis with any of those 

 described by such authorities as Sachs (' Lehrbuch,' pp. 180-184), 

 and Nageli ('Das Microscop,' pp. 612-623). The caulotaxis is 

 obviously cymose, but it can hardly be termed a dichasium, seeing 

 that the lateral branches do not develop equally, and that the 

 alternate ones become organised into a pseud-axis. Perhaps, 

 without doing much violence to the terms, it may be called a 

 pseud-axial dichasium. 



Occasional specimens of G. liohertianum present modifications 

 of this caulotaxis, which are both interesting and significant. One 

 or two of these may be noticed. 



If a large number of shoots be examined, some will probably 

 be found in which the development of the two-flowered peduncle 

 at the lower nodes has been arrested. It is seldom that more than 

 one or two nodes on an axis exhibit this apx^eartince, but where it 

 does occur, the absent peduncle is usually represented by a central 

 bud between the lateral branches. Very frequently, also, one 

 of the leaves at each node is much smaller than the other, and the 

 branches in the axils of the smaller leaves are but slightly 

 developed, or remain in the condition of a bud. When this 

 phenomenon presents itself the smaller leaves of successive nodes 

 are placed alternately on the pseud- axis. As an extreme case 

 of this, it may be mentioned that specimens are occasionally met 

 with in which only one leaf is present at the highest nodes, viz.^ 

 the one opposite to the peduncle. 



It will now be interesting to compare the caulotaxis of other 

 species with that of G. liohertianum. 



In 6r. iJiatcmc the leaves are opposite, and each bears a lateral 



