152 



THE CAUSES OF SPECIFIC SHAPE 



arrangement is maintained by the influence of the preformed parts, when 

 once the radial structure of the seedling has undergone its ontogenetic 

 conversion into the bilateral arrangement. The radial shoots of seedlings, 

 however, if removed as cuttings preserve their embryonic radial arrangement, 

 owing to the energetic influence of the preformed parts, and in this 

 condition form the plants with radially arranged needle-leaves known as 

 Rctinispora 1 (Fig. 25, a). These, while retaining their radial character, 

 may even produce occasional flowers and seeds. It is, however, hardly 

 surprising that, especially in old Retinispora plants, single or numerous 



bilateral Thuja shoots may appear (Fig. 25, b). 

 1) Such changes are due to alterations in the 



internal character, such as occur in a more 



pronounced degree when a root-apex turns 



into that of a shoot. 



Experiment has shown that cuttings do not 

 always retain the special character of the shoot- 

 system from which they are taken, and this is 

 only to be expected considering the disturbance 

 of the normal correlation produced by the re- 

 moval. That the radial shoots of ivy seedlings 

 acquire the adult bilateral structure, however, 

 when cultivated separately as cuttings, is a fact 

 well known to gardeners 2 , and without doubt 

 further investigations in this direction would 

 reveal numerous interesting facts. 



As in Thuja, the plagiotropic position 

 of the lateral shoots of Taxus baccata, Abies 

 pectinata, A. canadensis, &c., provides the condition for the development 

 of the aitionomic dorsiventrality. The buds are at first radial, and may 

 develop into radial shoots when a lateral axis grows vertically upwards 

 to take the place of the decapitated main axis. In the plagiotropic 

 position the orienting growth-movement of the needle-leaves produces 

 a two-rowed arrangement, the lessened growth of the upwardly directed 

 leaves results in a certain anisophylly 3 , and lastly the stem undergoes 



FIG. 25. Branch of Relinispora (a, a) 

 with Thuja shoots (b, b). 



1 Beissner, Gartenflora, 1879, P- IO 9! Handbuch d. Nadelholzkunde, 1891, p. 35; Beyerinck, 

 Bot. Ztg., 1890, p. 517 ; Goebel, Organography, 1900, I, p. 154. 



2 Beyerinck, 1. c., p. 535; Goebel,!. c., p. 161. For other instances see Hoffmann, Bot. Ztg., 

 1884, p. 214 ; Biisgen, Waldbaume, 1897, p. 224; de Vries, Die Mutationstheorie, 1901, p. 32. The 

 condition prevailing at the time of removal naturally influences the subsequent behaviour, so that it is 

 hardly surprising that plants developed from leaves of a Begonia which was ready to flower should 

 themselves flower earlier than usual (Goebel, 1. c., p. 46). Similar differences were observed by 

 Vochting (Jahrb. f. wiss. Bot., 1900, Bd. xxxiv, p. 102) in plants developed from cuttings taken 

 at different seasons of the year. 



3 Frank, Bol. Ztg., 1 868, p. 880, and Die naturl. wagerechte Richtung v. Pflanzentheilen, 1870, 



