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ON THE OAULOTAXIS OF BRITISH GERANIUMS. 

 By Thomas Hick, B.A., B.Sc. 



Perhaps it need hardly be said that the term caulotaxis is used 

 here in a sense analogous to that in which the words " j)hyllo- 

 taxis " and " anthotaxis " or "inflorescence," have long been 

 employed by botanists. The arrangement and relation of the 

 central and lateral axes of a plant are matters of some morpho- 

 logical importance, and for these the term caulotaxis will be found 

 at once definite and convenient. 



The caulotaxis of the Geraniums varies in different species, 

 and occasionally even in the same species, the modifications met 

 with in the genus as a whole sometimes presenting themselves 

 within the limits of a single species. In this attempt to elucidate 

 its essential features, it will be convenient to begin with what 

 is perhaps the commonest form, viz., G. liobertianum. As I write, 

 a shoot of this, collected quite casually, lies before me, and presents 

 the following organisation : — 



The lowest node present on the specimen bears two leaves, 

 which are placed opposite one another. In the axil of the left 

 of these leaves, as the specimen lies, is a lateral branch. But 

 between this lateral branch and w^hat appears to be the main axis 

 of the specimen is a peduncle bearing two flowers. At the next 

 higher node there are also two opposite leaves, and in the axil 

 of the right is a lateral branch. Further, between this lateral 

 branch and the apparent main axis, there is, as before, a peduncle 

 bearing two flowers. These characters are repeated at successive 

 nodes, except at the highest. Here there are two opposite leaves, 

 with a lateral branch in the axil of the left only, and the main axis 

 of the shoot runs directly forward and forms the common peduncle 

 of two flowers. 



This arrangement of leaves, central and lateral axes, and 

 flowers, may be easily represented diagrammatically, as in Fig. 1. 

 That the arrangement is not an accidental one, the examination 

 of a few specimens gathered at random will abundantly prove. 



Very little consideration is needed to show that the caulotaxis 

 described is of a very mteresting character. The position of the 

 flowers between what is a^oparently the main axis of the plant and 

 an axillary branch, will at once strike the eye as a peculiarity, 

 especially when viewed in connection with the terminal peduncle 

 at the highest node. But in this peculiarity we have the key to 

 the whole arrangement, for by its aid there is little difficulty in 

 making out that at the nodes, as well as at the apex of the stem, 

 the two-flowered peduncle is in reality a terminal structure. Thus 

 the peduncle met with at any node is a direct continuation of that 

 part of the main axis which forms the internode below. The 

 lateral shoot between the peduncle and the leaf on one side is an 

 ordinary branch developed in the axil of that leaf in a normal 

 manner, and presenting no noteworthy peculiarities. But what 

 appears to be part of the main axis on the other side of the 



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