66 



Elementary Botany 



overlapping is carried further (as in fig. iv.), it is said to be spiral 

 or twisted. 



(U) The separate leaves bent or rolled. — When, as in the 

 Columbine, involute leaves touch by their edges without over- 

 lapping (v.), the vernation is induplicate. When, as in the 

 Privet, conduplicate leaves are bent around one another (vi.), 

 it is eq^uitant ; whilst when, as in the Sage, they are only half 

 folded over one another (vii.) they are obvolute or half equitant. 

 When, as in the Apricot, a convolute leaf has another rolled 

 outside it (vui.), the vernation is supervolute. 



In considering branch- 

 ing, whether of root, stem, 

 or leaf, we must carefully 

 distinguish the main axis, 

 foot or podium, and the 

 branches. This, however, 

 is not always easy. 



I. In some cases the 

 main axis ceases to grow 

 when the branches are 

 formed. Such branching is 

 called dichotomy or dicho- 

 tomous branching. The 

 podium has at its extremity 

 two growing points, each of 

 which develops a branch. 

 Sometimes both of these 

 grow equally vigorously, 

 each bifurcating in its turn, 

 and a true dichotomy or 

 forked system is produced 

 (fig. 99, a). Sometimes one 

 branch becomes more 

 strongly developed than 

 the other ; the system now 

 becomes sympodial, the successive strong branches looking as 

 though they were the continuous axis, and the weaker branches 

 appearing to be lateral ones. If the stronger bifurcation is 



Fig. 99. — Diagrams of dichotomous branching. 

 Ai normal dichotomy, the forked branches 

 equally developed, and becoming the podia of 

 new dichotomies. B^ Bostrychoid dichotomy, 

 one fork-branch only becoming the podium of 

 a new dichotomy : in this case the left (/). C, 

 cicinnal dichotomy ; one fork branch, alternately 

 left (/) and right (?), becoming the podium of 

 a new dichotomy. B and C are sympodial 

 arrangements. (After Sachs.) 



