276 



METAMORPHOSIS 



of lateral branches ; on that subject we must refer to the special literature 

 concerned (Bravais, 1837-9 ; A. Braun, 1831 ; Hofmeister, 1868 ; Schwen- 

 DENER, 1878 ; GoEBEL, 1898), and merely point out that the general distri- 

 bution of the lateral members in the examples selected above is uniform on all 

 sides, so that we have before us a radially arranged growing point. As an 

 example of a bilateral growing point we may take that of Caulerpa holmesiana, 

 a unicellular alga (Fig. 68). The lateral buds arise in this case on two sides 

 only, i8o° apart, while the sides above and below, parallel with the plane of the 

 drawing, show no outgrowths. If we turn the body round through an angle of 

 90° we obtain an appearance like that shown at Fig. 68, //, where only the 

 bases of the lateral members are indicated. If we turn a radial growing point 



& 



JT 



Fig. 68. GTO'f,'\nzpo\nl of Caulerpa hohnesiaua. /.looked 

 at on face ; //, looked at laterally. After Reinke (1890). 



Fig. 69. Growing point 

 of a frond of Caulerpa 06- 

 scura. After Reinke(i8991. 



through 90°, or, in fact, through any angle, the appearance remains unaltered. 

 In Fig. 68 the lateral axes are arranged in pairs, the members of each pair 

 arising at the same level, and we term such an arrangement ' pinnate ' ; in so 

 far it corresponds to the whorled type of radial growing point. If, on the other 

 hand, the lateral branches be arranged in two alternate rows as in Fig. 69, we 

 have to do with the spiral type and may term it a one-half spiral. Looked at from 

 this point of view bilateral symmetry is merely a special case of radial. Dor si- 

 ventral symmetry is fundamentally distinct from 

 either of the preceding types (compare Goebel, 

 1880). As an example we may select the in- 

 florescence of Vicia cracca, where the whole of the 

 flowers arise on one side only (Fig. 70, /), while the 

 other side has no outgrowths at all (Fig. 70, 2). We 

 do not distinguish in this case two flanks but a front 

 and back. The arrangement of the lateral organs 

 individually is of the greatest interest. They are 

 arranged in regular parastichies as on a radial 

 growing point and we could number the organs in 

 this case also were it not that they early assume a unilateral arrangement. 

 We see, however, that unilateral development does not preclude an essentially 

 spiral taxis, confirming the conclusion already come to that the ' fundamental 

 spiral ' has no significance of any importance. 



We must now consider the form of the growing point. In the examples 

 hitherto given it takes the form of a slender paraboloid, or, as it is generally 

 termed, though less accurately, a cone. Very frequently, however, it has the 

 shape of a flattened cone or disc. We meet with such forms not infrequently in 



Fig. 70. Inflorescence of Vicia 

 cracca. i. Front view ; 2, back 

 view. After GoEBEL(i88o, PI. X, 

 Figs. 19 and 20). 



