282 M. WICHURA ON THE WINDING OF LEAVES. 



Fam. of the Myrtaceae — and Acacia 7nicracantha,Desv. (see fig. 7) 

 — Fam. of the Mimoseae — have the stem-leaves vv^ound in a helix 

 turning sometimes to the right, sometimes to the left, making 

 the helix by connecting the points of insertion of the leaves on 

 the stem, from below upwards, by the shortest line. In like 

 manner are the distichous or many-ranked verticillately-arranged 

 leaves of Pinus, e, g, P. sylvestris, L., P. Pinea, L., P. excelsa. 

 Wall., P. MughuSy Scop., &c., determined in the direction of 

 their winding by the direction of the helix which is described by 

 the succession of scales at the base of each fascicle of leaves. 

 The direction of this helix constantly agrees with the direction 

 in which the leaves wind. The reverse occurs in the petals of 

 Gillenia trifoliata, Moench. — Fam. of Rosaceae; the Silenece 

 with three or several styles, e. g. Silene, Lychnis, Viscaria, Cu- 

 cubalus ; as also in the species of Hypericum, Geranium, Linum 

 and Oxalis, which in their contorted aestivation are wound in a 

 direction contrary to the readily distinguishable spiral of the 

 sepals. Probably the sometimes right-, sometimes left-wound 

 flower-buds of Statice, Fam. of Plantagineae, — Lysinema, Fam. 

 of Epacrideae, — Cistus, Fam. of Cistineae, — Lavradia ericoides, 

 A. St. Hil., Fam. of Sauvagesieae, — Bombax, Helicteres, Fam. 

 of Sterculiaceae, — Hermannia and Mahernia, Fam. of Byttne- 

 riaceae, — Maronobea globulifera, L., Fam. of Clusiaceae, — Rici- 

 nocarpus pinifolia, Desf., Fam. of Euphorbiaceae, — and the 

 Malvaceae, are in like manner dependent on the direction of 

 the forerunning leaf-spiral. There is great difficulty, however, 

 in making out these, and I have not yet succeeded in deter- 

 mining their direction*. 



§46. 



5. Unlike lateral insertion of verticillate Leaves, 



Chironia frutescens, 1j,, Ch, grandiflora, Fam. of Gentianeae : 

 — stem-leaves in binate whorls. The leaves of the individual 

 whorls are wound in the same directions, the leaves of alternate 



* The connection between the direction of the contorted aestivation and the 

 arrangement of the leaves was explained by Alexander Braun so long ago as 

 the year 1838, before the Naturforscher-VersammluiKj at Freiburg, Breisgau. 

 — See A. Braun, On regular rotation (or twisting) in the Vegetable Kingdom. 

 Flortty 1839, i. 311 et seq. 



