184 Le Goc. — Observations on the Centripetal and Centrifugal 
reduit alors qu’il s’y est ddveloppe un tissu ligneux sapp Ilmen taire centri- 
pete . . .’ 1 He then refers Cycads to the Poroxylon type. 
The difficulty of deciding among these various interpretations led 
Chodat to suggest a reconsideration of the whole problem. 2 I would not 
have ventured to undertake a part of this difficult task if Professor Seward 
had not invited me to do so and encouraged me during the investigation. 
I wish to take this opportunity of expressing to him my hearty thanks for 
his kind interest and advice during this work. The material, with the 
exception of a frond for which I am indebted to the Director of the Royal 
Gardens, Kew, was obtained from the Botanical Garden, Cambridge, and 
generously supplied by Mr. Lynch, the Curator, to whom also many thanks 
are due. 
Five genera of Cycads, including seven species, and as far as possible 
of different ages, have been examined: Cycas circinalis and C. revoluta , 
Stangeria par ado xa^ Dioon edide , Ceratozamia mexicana , Encephalartos 
horridus and E. villosus. 
The observations recorded in this communication were limited to the 
Cycadean leaf, and are restricted to the relation of the centripetal and 
centrifugal xylems to one another, and the relation of both to other tissues, 
these relations form the crucial point of the whole problem. 
It was not until a preliminary account of my investigations had been 
written that I discovered a paper much on the same lines by Dr. Carano, of 
Rome. This paper, which is very detailed, has not perhaps received all the 
attention it deserves. 3 
Observations . 
My observations lead me to conclude that the sketches and plates 
published do not usually represent the structure of a vascular bundle such 
as is found at the very base of a Cycad. This is, however, of great impor- 
tance, as it is there that the most interesting changes occur ; the transition 
from the stem-type of xylem into the petiolar arrangement of that tissue is 
seen along a few centimetres of petiole which immediately follow the stem. 
The shoot of a fully developed petiole of a Cycas is first described as 
a basis for subsequent discussion. A few bundles pass into the leaf at the 
junction of petiole and stem. Their number varies much, but there are at 
least two main bundles to which the secondary ones seem to be related. 
These secondary bundles sometimes reunite with the main one, forming 
loops, before the latter begins to branch rapidly and forms part of the well- 
known large 00 set of bundles which will run up the petiole. This 
happens, say, at 1 cm. above the junction with the stem. 
From our point of view the main bundles are the important ones, for 
they remain fairly constant for a distance of 2 cm. or 3 cm., even while they 
1 C. Eg. Bertrand (’86). 2 R. Chodat (’08). 3 E. Carano (’03). 
