the Sieve-tubes in Laminar ieae. 1 1 3 
sieve-tubes 1 . It is only necessary to quote the beautifully 
developed sieve-tubes in Cucurbita , Lagenaria , Vitis , Hamu- 
lus, Tamus communis , etc., which are conspicuously wider, and 
have wider perforations than in the generality of other 
Phanerogams. So in Macrocystis and Nereocystis . In these 
alone of all the Laminarieae we find true sieve-tubes, and 
these with very large plates with wide pores ; and in addition 
to this, the perfection of the mechanism by a callus-develop- 
ment. The causes necessitating the presence of such highly 
developed organs for the transport of plastic substances are, 
there can be little doubt, in both cases much the same. 
In conclusion, I think it must be fairly obvious that in these 
two plants we have to deal with what may be considered a well- 
differentiated vascular bundle — at least so far as the phloem 
is concerned. That this bundle is in any way homologous 
with that of higher plants is a matter beyond the province of 
this paper to discuss. Indeed, I believe rather the line of 
descent of higher plants to have diverged long since from the 
stock from which the L aminarieae arose. 
To me one of the more interesting results of this investiga- 
tion is to confirm the opinion of systematists as to the close 
affinity existing between the genera Macrocystis and Nereocystis , 
although there is a considerable diversity of external form. 
In the great treatises on Algae 2 they are united closely 
together, although the determination was not based on their 
internal structure, of which little was known at the time ; nor 
on their reproduction, concerning which nothing is known in 
Nereocystis , and in Macrocystis the presence of £ spores 5 on 
late-arising adventitious shoots or leaves in the neighbourhood 
of the root is all that has been ascertained 3 * . It remains then 
a most interesting point to solve the mode of reproduction in 
these two genera, and to see how far their agreement bears out 
their near affinity as based on the minute structure of their 
1 G. Haberlandt, Physiologische Pflanzenanatomie, p. 222. 
2 Kutzing, Species Algarum, p. 584. 
3 Cf, W. Gardiner, On the occurrence of reproductive organs on the root 
of Laminaria bulbosa , in Proc. Camb. Phil. Soc. Vol. v (1885), p. 224. 
