234 CONTRIBUTIONS TO 
tyledons, mm the leaf, stem, and their metamorphosed parts. 
The largest which I have seen measured 0:0022 Paris inch in 
diameter (in Fritillaria pyrenaica) ; the smallest, im the em- 
bryonal extremity of the pollen-tube of Linum pallescens, from 
0:00009 to 0-0001 Paris inch. In the albumen of Abies excelsa 
I found the average of several admeasurements of examples, 
which appeared of equal size, to be 0:00034:-0-00059 -0:00079. 
In the young leaves of Crussula portulaca, 0-0003; and in the 
albumen of Pimelea drupacea, 0:00095-0:001055. Little im- 
portance, however, can, on the whole, be attached to these 
admeasurements, since they increase and diminish, and we 
cannot determine in what period of its existence the cytoblast 
may be at the time. 
Its internal structure is in general granulous, without, how- 
ever, the granules, of which it consists, being very clearly dis- 
tinct from each other. Its consistence is very variable, from 
such a degree of softness as that it almost dissolves in water, 
to a firmness which bears a considerable pressure of the com- 
pressorium without alteration of form. The more recent its 
formation, the softer it is; and this also applies to cases in 
which its existence is merely transitory. It is denser and more 
sharply defined when it endures throughout the whole vital 
process of the plant as a permanent tissue, as in the Orchidee. 
These peculiarities have been more or less fully described 
by R. Brown (Organs and Mode of Fecundation in Orchideze 
and Asclepiadez ; Linn. Trans. 1833, p. 710), and recently by 
Meyen (Physiologie, &c., Bd. I, p. 207). A phenomenon, how- 
ever, has escaped both of these most acute observers, which I 
am notwithstanding disposed to regard as one of the most 
essential. In very large and beautifully developed cytoblasts, 
for example, in the recently formed albumen of Phormium 
tenax and Chamedorea schiedeana (pl. I, fig. 5), there is ob- 
served (whether sunk in the interior or on its surface, is not 
yet clear to me) a small, sharply defined body, which, judging 
from the shadow that it casts, appears to represent a thick 
ring, or a thick-walled hollow globule. In examples which are 
not so well developed, only the external sharply defined circle of 
this ring can be observed, and in its centre a dark point; for 
example, in the stipes of the embryo of Limnanthes Douglasii, 
Orchis latifolia (pl. I, fig. 21), Pimelea drupacea (figs. 14, 15). 
