298 Dr. H. Airy on Leaf -Arrangement. [Apr. 30, 



In two uteri menstruation was imminent, but the flow had not begun. 

 In these the mucous membrane of the body of the uterus was fully deve- 

 loped, and had begun to undergo fatty degeneration. There was a 

 marked distinction between it and the muscular tissue throughout the 

 uterine cavity : it was highly congested. . 



In one uterus the menstrual flow had taken place for one day, and in 

 another for two or three days before death. In these there was extrava- 

 sation of blood into the mucous membrane, and the latter had in part been 

 disintegrated and removed. 



Menstruation appears essentially to consist, not in a congestion or a 

 species of erection, but in growth and rapid decay of the mucous mem- 

 brane. The menstrual discharge consists chiefly of blood and of the 

 debris of the mucous membrane of the body of the uterus. The source 

 of the haemorrhage is the vessels of the body of the uterus. The mucous 

 membrane having undergone fatty degeneration, blood becomes extrava- 

 sated into its substance; then the membrane undergoes rapid disinte- 

 gration, and is entirely carried away with the menstrual discharge. A 

 new mucous membrane is then developed by proliferation of the inner 

 layer of the uterine wall, the muscular tissue producing fusiform cells, 

 and the groups of round cells enclosed in the meshes of the muscular 

 bundles producing the columnar epithelium of the glands. 



II. "On Leaf-Arrangement." By HUBERT AIRY, M.A., M.D. 

 Communicated by CHARLES DARWIN, F.R.S. Received 

 March 23, 1874. 



(Abstract.) 



This paper is offered in correction and extension of the views con- 

 tained in a previous paper by the same author, read 27th February, 

 1873. 



The main facts of leaf-arrangement to be accounted for are : 



(1) the division into verticillate and alternate leaf-order; 



(2) in the former, the equal division of the circumference of the stem 



by the leaves of each whorl, and the alternation, in angular posi- 

 tion, of successive whorls ; 



(3) in the latter, the arrangement of leaves in a spiral series round the 



stem, with uniform angular divergence between successive leaves, 

 and the limitation of that angular divergence (represented as a 

 fraction of the circumference) to certain fractional values (in most 

 cases only approximate) which find place most commonly in the 

 following convergent series (A) : 



1 1 2 3 5 8 13 21 34 55 o ,^ 



V 3' 5* 8' 13' 2T 3T 55' 89' 144' &C< '* W 



