272 PHYSIOLOGICAL BOTANY. 



expression emanates from Ehrhart, and signifies the pre- 

 sence of both calyx and a corolla. The word is well con- 

 structed. P. externum signifies the calyx, P. internum 

 the corolla ; hence the expression may be conveniently 

 used where an intermediate form is present, as in many 

 of the Monocotyledons, especially, however, in the Thy- 

 meleacese, the Polygonacese, &c., for the true calyx of a 

 Chenopodium is very different in structure from the calyx 

 of the corolla of a Daphne. 



Disquisition upon a Problem propounded in Phyllotaxy. 

 By ANTON. PHESTRANDREA. Messina, 1843. A. M.Argen- 

 tano presented for solution, in a journal (Interprete Ann., 

 iv, No. 7), a problem in the theory of the arrangement of 

 leaves, and it is very satisfactory to find that this German 

 theory has travelled as far as Sicily ; which would cer- 

 tainly not have been the case, if the excellent report of 

 Martius and Bravais had not appeared in the ' Annales 

 des Sciences Naturelles.' The problem is as follows : 

 In a plant, the arrangement of the leaves of which is 

 spiral, the spiral winds 13 times around the stem, and 

 the angle of divergence amounts to 137^ degrees ; to find 

 the number of leaves or foliar organs which compose the 

 cycle. The solution is very simple. If we denote the 

 angle of divergence by d, the number of turns by a, the 

 number of foliar organs in the cycle by m, we have, ac- 

 cording to Schimper, d = , in which we may 



m 



denote one of the three magnitudes an unknown oc. We 



Qn* 1 ^ 



then have 137+ 11= ou , whence (137 + $ x = 



ft 



360-13, and therefore x= 34. The object is to bring 

 Schimper's theory under consideration (although Al. Braun 

 only is mentioned), in which the divergence of the gene- 

 rating spiral is assumed as 137^ degrees, according to 

 Bravais. The author comments at some length upon the 

 aid which one science can afford another ; as an instance 



