94 



ESSENTIALS OF VEGETABLE PHARMACOGNOSY. 



and still higher \ip the whorled arrango- 

 ment may be lost, the leaves becoming ar- 

 ranged as in the form next considered. 



By the other arrangement the nodes 

 produce solitary leaves, so that each leaf 

 is successively produced at a higher level. 

 If a line be traced from the point of 

 origin of one leaf to that of the one :iext 

 above, and continued in the same direc- 

 tion, so that it exactly meets the point of 

 insertion of another, and then of another, 

 and so on, it will at length meet one ex- 

 actly over the point of starting — that is, 

 find that either one or more than one leaf a second leaf in the same Orthostachy 

 is developed from a node. In the latter (pj^^ 48I), It will then be found that 

 case the arrangement is called Verticil- 

 lute or Whorled, and the circle a Whorl 

 or Verticeh If the Whorl contain but 

 two members, they are called Opposite — 



PHYLLOTAXY. 



In view of the established fact that the 

 develo*pment of the branches follows that 

 of the leaves, it becomes clear that the 

 arrangement of the latter determines the 

 entire symmetry of the plant, with all the 

 far reaching consequences in connection 

 with both vegetation and reproduction. 

 Certain definite laws of phyllotaxy hav- 

 ing been ascertained, the forms result- 

 ing become, in their different manifesta- 

 tions, of nearly fundamental importance 

 in classification and in diairnosis. We 



the line followed is a spiral, which has 

 passed once or more around the stem. 

 Such a spiral is called a Cycle, and if its 

 line be continued it will form other sini- 

 that is, the centres of their points of in- ijar cycles above and below. It is ob- 



sertion are separated by one-half the cir- 

 cumference, or their Divergence is ISO 

 degrees. Usually the other nodes are 

 similarly clothed, except that in all of the 

 higher plants the leaves of each pair De- 

 cussate with those of each adjacent 

 pair^-that is, a leaf of one whorl is over 

 the centre of the sinus of that next below 



served that a cycle will be limited by two 

 adjacent leaves of one Orthostachy. 

 Thus, if leaf No. 4 is the next in the 

 orthostachy, to which leaf No. 1 be- 

 longs (Fig. 4S2), three leaves will belong 

 to that cycle. A cycle containing three 

 leaves makes but one turn of the stem. A 

 cycle is expressed in the form of a frac 



and that next above (Fig. 479). Four ^ion, its numerator indicating the number 

 vertical rows (Orthostachies) of leaves 



thus appear upon such a stem (Fig, 480). 



If, instead, there be three leaves to the 



of times it encircles the stem, its denom- 

 inator the number of leaves which it in- 



whorl, six orthostachies will result; if 

 four, eight; and so on. It frequently 

 happens that the number of leaves in the 



eludes, so that the cycle last described 

 must be indicated by the fraction one- 

 third. If the next leaf in the same 

 orthostachy as No. 1 be No. G (Fig, 483), 



upper or lower whorls will contain only ^i^^^ that cycle will contain five leaves, 

 half the number of leaves in the others, ^ ^j^i^ containing five leaves makes two 



