1094 
Thompson . — The Anatomy and 
E. monostachya , shows a very early development of several broad rays. 
Some of them which lack cell contents are to be distinguished as areas in 
which there are no vessels. As a rule, however, the broad rays do not 
appear until a considerable zone of wood has been formed. 
With the increase in circumference of the young stem the rays become 
proportionately broader. If the increase went on indefinitely the rays 
would soon become too broad for the proper organization of the stem 
tissues. In Ephedra the stems rarely become large enough to cause this 
difficulty, but when they do it is met by the secondary obliquely vertical 
division of the rays. In tangential view the rays are found to be divided by 
oblique strands of fibres into a number of segments which then become 
scattered horizontally through the wood, as the strands of fibres increase in 
size. This division of broad rays with the increase in diameter of the stem 
is similar to that described by the writer 1 as occurring in certain of the 
Fagaceae and Casuarinaceae. Zilztra 2 has observed the same phenomenon 
in several Dicotyledonous plants. It was used in the former contribution in 
support of the theory that the smaller multiseriate rays of the Dicotyledones 
have been derived from the broad aggregate ray by the diffusion of the 
latter throughout the wood. In Ephedra the stems rarely become large 
enough to make the dissection process a necessity, but its occasional 
presence shows that the same rule holds as in the Dicotyledones. 
Bailey 3 has shown that oak wood formed immediately after an injury 
is likely to present primitive conditions of ray structure. In such areas one 
may find only uniseriate rays, and these later undergo the compounding 
process to form broad rays again. These phenomena are in agreement 
with the well-established principle that traumatic areas tend to revert 
to primitive conditions. In Ephedra such a reversion is extremely rare, 
although it is occasionally to be seen. For the most part, however, wound- 
ing has very little effect on ray structure, the rays continuing about the same 
size as before the wound. Occasionally, indeed, the wound causes the 
enlargement of rays already present, and even the introduction of new ones. 
As Bailey has suggested for a similar phenomenon in the oak the wound 
appears in these cases to stimulate the development of broad rays. On the 
whole, however, the effect of wounding is very indefinite. 
One other respect in which the rays of Ephedra resemble those of the 
Dicotyledones is their retarding effect on the growth of the stem. In 
the oak the growth is slower in the vicinity of the broad ray, and the result 
is manifested in a distinct ‘ dip ’ in the contour of the annual rings which 
1 Thompson, W. P. : Origin of the Multiseriate Ray of the Dicotyledons. Ann. Bot., October, 
I911. 
2 Die Gestalt der Markstrahlen im sekundaren Ilolze. Recueil des Travaux Botaniques Neer- 
landais, vol. v, 1908. 
8 Bailey, I. W. : Reversionary Characters in Traumatic Oak Woods. Bot. Gaz., Nov., 1910. 
