[ 267°] 
XIII. The Longitudinal Symmetry of the Centrosperme. By PERCY Groom, M.A., 
D.Sc., F.L.S., Assistant Professor of Botany, Imperial College of Science and 
Technology, London. 
(26 Text-figures.) 
Read 21st January, 1909. 
IN my preliminary communication to the Linnean Society and my paper published in 
the * Transactions’ of the Royal Society (1908) I suggested a graphic method of recording 
the longitudinal distances apart of the successive leaves of a shoot. According to this 
method the successive segments of a stem are recorded on squared paper as successive 
ordinates, and the resultant curve is termed an “ internode-curve." 
The application of this method to a typical stem shows an unexpected regularity, 
and relative constancy, in the internode-curve in a species ; the internode-curve of the 
main axis assumes an ascending-descending (normal) form, while those of the successive 
branches (proceeding from the base to the apex) exhibit a gradual echange from the 
ascending-descending form to a purely descending one. But in the Chenopodiacez, 
while the opposite-leaved Salicornia shows typical internode-curves, the alternate-leaved 
types are characterized by peculiar zigzag internode-curves, which, when analysed by 
joining the alternate ordinates, each yield two regular or consistent subeurves. It was 
shown in my previous paper that the zigzag internode-curve is probably due to the 
longitudinal diremption of the originally opposite leaves at each of the nodes, and that 
the two subcurves represent respectively an internode-subeurve and a displacement- 
subcurve. 
In the present paper are recorded additional observations showing the general 
prevalence of this type of longitudinal symmetry in the alternate-leaved Chenopodiacere. 
The observations concern: on the one hand, numbers of individuals of one species, and 
the different axes (primary to quaternary), in order to show the range of variation in one 
species and yet the universality of the two subeurves ; and, on the other hand, additional 
species. j 
The fact that the Caryophyllaces are almost without exception xou 
and that the majority of the other families of the Centrospermee include m m 
alternate-leaved types or opposite-leaved types only, suggested that possibly p vica 
phyllotaxis of the Centrosperme as a whole was opposite m type, and that throug a 
the cohort the alternate phyllotaxis was derived en bs by leaf-displacement. e 
Present investigation is also designed to test this possibly. —— 
eg were made on E T Caryophyllaceæ, Aisoaceæ. Amarantacem, 
Phytolaccaceæ, and Portulacaceæ. 9s 
SECOND SERIES.—BOTANY, VOL. VII. 
