Hydrodictyon utricu latum . - 633 
the evidence in favour of it is not sufficient to be convincing. 
The fact that the pyrenoid is a temporary structure does not 
certainly disprove the truth of the suggestion, for, as Eberdt has 
maintained, it is possible that the leucoplast may arise de novo 
in the cell. It is perhaps more difficult to think of a leuco- 
plast and chloroplast as associated together in the same cell. 
Such an association would certainly be out of harmony with 
the doctrine of the genetic relations of the two organs as 
maintained by Schimper. The most serious objection, how- 
ever, to the comparison suggested by Boubier seems to me to 
lie in the fact of the difference in structure between the 
pyrenoid and leucoplast. So far as I have been able to ob- 
serve, it is by no means easy to differentiate the leucoplast 
from the rest of the protoplasm by the ordinary methods of 
cytological research, such as those used in the present investi- 
gation ; and when it is differentiated, it has a granular or reti- 
culate appearance, while the pyrenoid appears homogeneous, 
dense, and sharply bounded. 
The method of starch-formation in the pyrenoid as I have 
described it has, so far as I can determine, no analogy with 
that in the leucoplast — at least so far as its functional aspects 
are concerned — with the possible exception that, as main- 
tained by Eberdt 1 and Schimper 2 , there is a breaking down 
of a proteid substance to form a carbohydrate 3 . 
Should the conclusions of Meyer 4 and Salter 5 , that starch- 
formation in the leucoplast is a process of secretion within the 
body of the leucoplast itself, without involving any change in 
its structure, prove correct, Boubier’s hypothesis would be 
1 Beitrage zur Entstehungsgeschichte der Starke ; Jahrb. f. wiss Bot., Bd. xxii, 
p. 293. 
2 Untersuchungen liber das Wachsthum der Starkekorner ; Bot. Ztg., Bd. xxxix, 
1881, p. 185. 
3 The difference between these two authors lies not in the method of starch- 
formation itself, but in the nature of the body in which it is formed. Schimper, as 
is well known, maintained that it is a permanent cell-organ, while Eberdt thought 
it to be a temporary body consisting of what he called starch ground-substance, 
which was entirely converted into starch. 
4 Untersuchungen liber die Starkekorner. Jena, 1895. 
‘ Jahrb. f. wiss. Bot., Bd. xxxii, 1898, p. 117. 
