99 



of space not being able to go more deeply into the doctrines 

 of this work, which shall be done in next year's report, if in 

 the mean time no other person shall have taken up the sub- 

 ject. 



The profound researches of L. and A. Bravais * respecting 

 the arrangement of the leaves have excited in the past year 

 particular attention, especially on account of the difference in 

 the exposition and in the results from the similar inquiries of 

 German botanists. Several new terms have been added to 

 the existing nomenclature in reference to this subject which I 

 shall commence with. Secondary spires are those multiple par- 

 allel spires which by their union embrace all the leaves ; the 

 number of these spires is called the secondary number, and the 

 divergence separating two consecutive leaves of one of these 

 spires, the secondary divergence ; thus, when parallel and equi- 

 distant spires suffice to embrace all the leaves, eight will be 

 the secondary number of these spires. By ; encyclical number is 

 understood the number of circumvolutions requisite for the 

 primitive spire to pass from one leaf to the next following of a 

 secondary spire. For the sake of shortness the expressions dex- 

 trorsum and sinistrorsum are frequently replaced by their ini- 

 tials D. and S. : thus 2 S. represents a system of two parallel 

 spires comprehending all the leaves and proceeding from right 

 to left ; 3 D. a system of three dextrorsal spires, and so forth. 



Although the leaf and the vital node are two decidedly di- 

 stinct organs, yet they are not here separated ; and frequently 

 the word insertion is employed, which has the advantage of 

 being equally applicable to the leaf and to the various foliaceous 

 organs, such as the scale, bract, &c. derived from it. Mother- 

 leaf is that leaf in the axilla of which any of these parts may 

 have originated. The authors divide the leaves into two differ- 

 ent groups; 1. curviseriate, arranged on all sides in spiral lines, 

 never forming vertical series, each leaf being the only one on 

 the vertical containing it ; 2. rectiseriate, capable of forming 

 series parallel to the axis of the stem. 



The memoir is divided into two chapters ; in the first the 

 geometrical laws of the spirals are developed, and in the second 



* Essai sur la disposition des feuilles curviseri^es. Annal. des Scienc. 

 Nat. Bot. p. 42- 120. 



H2 



