( 27 ) 



PHYLLOTAXIS. 



As the buds grow from the axils of the leaves, their arrangement is the 

 same as that of the leaves. They are either opposite or alternate. 



When the buds are opposite, one pair stands transversely to the next 

 lower, so that, when seen from above, the four buds form a cross, as do also 

 the leaves and the branehlets ; the third pair corresponds to the first one. 

 This position is called decussate, and we find it in the species of Euonymus, 

 Staphylea, Aesculus, Acer, Negundo; Hydrangea, Cornus (^ except C. aller- 

 ni/oliuh), Lonicera, Sambucus, Viburnum, Bignonia, Tecoma, Fraxinus, 

 Foresteria. 



A whorl of three buds we find in Catalpa, and also usually in Cephal- 

 anthus (sometimes four or only two). Each whorl alternates with the next 

 one, so that, seen from above, a whorl of six is formed. In all the rest of 

 our woody plants the buds are alternate. Though seemingly irregular they 

 are arranged in a definite order. The buds are alternate in two lines 

 (bifarious), or in other words the third bud corresponds to the first, the 

 second to the fourth ; two buds make one circuit, and this is expressed by 

 the fraction i ; the numerator indicates the circuit, the denominator the 

 number of buds. This arrangement we find in the species of Asimina, 

 Vitis, Ampelopsis, Cercis, Hamamelis, Brunnichia, Dirca, Ulmus, Celtis, 

 Morus and Smilax. 



In Betula and Alnus three buds make one circuit in a spiral line ; the 

 fourth bud stands above the first (5 ). 



In the majority of our woody plants five buds make two turns in a spiral 

 line, and the sixth bud stands above the first (two-fifths). In the oaks the 

 upper buds are somewhat crowded. The beech and Tilia, though properly 

 belonging here, have the buds on the horizontal branches in two oppo- 

 site lines. 



There is one little tree {Pieleu) with eight buds in three circuits (i 1, 

 and one shrub {Amorpha fruticosa), with thirteen buds in five circuits (five- 

 thirteenths). In Pthamnus four buds make one circuit, but the merithalls* 

 between the first and second and the third and fourth, are much shorter than 

 between the second and third ; and as we sometimes find the pairs of buds 

 in Euonymus and Fraxinus displaced ( one higher than the other), we may 

 conclude that Rhamnus belongs to the same division as those. The position 

 is properly decussate. The same conclusion we may make in regard to the 

 elm, the seedling of which has opposite leaves ; and perhaps we may ex- 

 plain the bifarious position of the buds on the branches by a (hypothetic ) 

 torsion of the merithalls. 



The best way to count the buds and their circuits, is to thrust a pin 

 into each leaf-scar at a right angle to the stem, and attaching a thread 

 to it, pass this from the lower to the next higher until the one is reached 

 which corresponds to the first one. 



Figures 18 — 21 on PI. IV show in diagram the phyllotaxis of four 

 different woody plants. The figures represent the bark split longitudinally 



*Intemodes. 



