1 82 Johnson . — The Nursing of the Embryo 
contain a great deal of sugar. Owing to the parasitism of M. 
punctulatum , the function of the sieve- tubes is very probably 
different from that in independent plants. The formation of 
proteids from carbohydrates, sulphates, and nitrates in the 
non-nucleated sieve-tubes of these plants is not required of 
the sieve-tubes of Myzodendron , which is supplied by its host 
with proteids ready-made. Its nucleated sieve-tubes are 
probably active, mainly, in the formation of sugar for the 
thickening of the xylem vessel walls, etc. It would be of 
considerable value to have a comparative knowledge of sieve- 
tubes in parasites, in their bearing on this particular point. 
In the whole vascular tissue of the stem there is a dia- 
grammatic regularity of arrangement of the parts, the re- 
lation of the secondary tissue to the cambium being very 
clear. In a stem inch in diameter the position of the 
groups of primary phloem is still marked, partly owing 
to the production of secondary phloem on their inner side 
being greater than elsewhere, and partly owing to their crushed 
condition. Periderm is formed from the superficial layer of 
cortex, lenticels are present and, in keeping with the horizontal 
position of the stem, are, as pointed out in the Flora Antarctica, 
more numerous on the under side. No clearer example of the 
beginning of the formation of periderm beneath stomata in 
stems could be desired than that of M. punctulatum. My first 
impression was that the periderm was localised, confined to 
the region of the stomata, cutting them off as they became 
functionless, but not extending further so as to form a com- 
plete zone since the secondary thickening was slight and 
slow. The branching of M. punctulatum is sympodial. 
Each branch elongates by apical growth for one year only; 
a twig at the end of its first year’s growth is one to two 
inches long, and bears nine to twelve spirally arranged 
scale-leaves with relatively long internodes. The punctum 
vegetationis, which is usually a little awry, consists of a 
blunt axis ensheathed in several closely-packed leaves. 
So far as further growth is concerned this punctum vege- 
tationis is barren, its meristematic tissue being dead and 
