DORSIVENTRAL CREEPING AND CLIMBING SHOOTS 



shoots upon the flanks, and ' roots ' upon the ventral side. The relation- 

 ships of position which occur in the creeping stems of Marsilia and 

 Pilularia, among the Filicineae, are similar. Other creeping stems of 

 ferns, like those of Lygodium palmatum, Polypodium Heracleum, and 

 Polypodium quercifolium l , have the dorsally-placed rows of leaves so 

 near one another that they appear as if there was only one row, whilst 

 in Polypodium taeniosum the parastichies of leaves stand close together 

 on the dorsal side only. The germ-plants of Polypodium Heracleum, 

 which were investigated by Klein, have a distichous phyllotaxy with 

 a divergence of the rows of about 45 upon the dorsal side, so that the 

 dorsiventrality is less sharply marked in them than in the older plants 

 which have a monostichous or 

 nearly monostichous phyllotaxy. 

 In all these ferns the dorsiven- 

 trality is already fixed at the 

 vegetative point and is not the 

 result of subsequent displace- 

 ment. The lateral shoots of 

 these ferns are placed nearly on 

 the flanks. Analogous relation- 

 ships of position are also found 

 among flowering plants, in species 

 of Begonia, for example, with 

 thick fleshy creeping stems ; the 

 Podostemaceae also, which cling 

 to their substratum, often show 

 dorsiventral construction 2 , and 

 other examples will be occasion- 

 ally mentioned in the course of 

 this account 3 . 



FIG. 47. Caulerpa prolifera. Habit. The creeping shoot- 

 :is (a) hears leaves (0,1 above and roots (r) below. Lehrb. 



The facts which have been 

 mentioned should suffice to show 

 how widely spread dorsiventral 



construction is in creeping and climbing plants in the most different cycles 

 of affinity ; and it is clearly the most advantageous one, for the leaves 

 through their situation on the dorsal side are exposed to the light most 

 simply and without any torsions being necessary, origin on the ventral side 

 is the best for the roots, and as the whole shoot is pressed to the sub- 

 stratum the position of the twigs upon the flanks is manifestly fitting. 



1 See with reference to the species of Polypodium L. Klein, Ban und Verzweigung einiger dorsi- 

 ventral-gebauter Polypodiaceen, in Nova Acta Acad. Leop.-Carol. xlii. Halle, iSSi. 



2 See Warming's account of this family, also my ' Pflanzenbiologische Schilderungen,' ii. p. 331. 



3 The case of Nuphar luteum has been mentioned on p. 85. 



