ig8 Peculiar Growth Habit and the Anatomy of Dog’s Mercury . 
In this species the buds in the axils of the leaves of the 
aerial shoot do not normally produce lateral shoots, and all 
vegetative growth occurs in connection with the apical 
rneristem. It is interesting to note, however, that a number 
of plants were observed in September which had been 
decapitated earlier in the year and had produced vigorous 
vegetative shoots from the axils of the first pair of leaves 
below the inflorescence region. This is interesting, because 
in species in which the terminal rneristem ceases to exist as a 
result of flowering, growth continues by development of 
lateral shoots; in this case, however, the same result follows 
the extermination of the apical rneristem by some external 
agency. 
Another interesting observation was made on December 
28th, 1932. The winter up to this date had been particularly 
mild and many Mercurialis plants in sheltered positions still 
had a living aerial shoot. Two such plants were discovered 
on which the last two pairs of leaves at the apex had axillary 
inflorescences. These plants had gone through the normal 
cycle of development, ending with the production of leaves 
without axillary inflorescences at the apex of the stem, and 
had then become active again and produced more leaves with 
inflorescences. This may be accounted for by the mild 
weather. The rneristem, not being killed, resumed growth 
under conditions of high soluble carbohydrate favourable to 
flowering. 
Some Notes on the Anatomy of Mercurialis. 
As the shoot elongates in spring protoxylem (cut off from 
the cambium) and phloem differentiate rapidly, and at this 
time large numbers of sieve tubes still containing nuclei are 
to be found in all parts of the stem and in the leaf petioles 
and inflorescence stalks. After the elongation of an internode 
has ceased, metaxylem is formed, but protoxylem still 
differentiates in the elongating internodes above as was 
recorded by Thoday for sunflower. 4 After the rapid elonga- 
tion of the shoot, phloem differentiation becomes slow, but 
some sieve tubes containing nuclei were always to be found 
near the cambium. Further differentiation of phloem occurred 
in the stem after fruiting, probably in connection with the 
downward transfer of food from the leaves to the storage 
tissues of the underground stem. In the inflorescence axis of 
the female plant a small amount of xylem and phloem are 
added as the fruits develop. 
In an elongating internode of the shoot the vascular tissue 
is arranged in eight bundles. After elongation has ceased 
the bundles become joined by the development of an inter- 
fascicular cambium from which are produced two to eight 
The Naturalist 
