the Sieve- tubes in Laminar ieae. 1 1 5 
point out that their distribution, relation to the sieve-plates, 
and various stages of development in tubes of varying age 
(bearing, as they do, such a striking similarity to what occurs 
amongst Phanerogams) entirely precludes their being due to 
any such chance cause. They are no doubt as natural and 
essential a part of the sieve-tube mechanism of the plants in 
question as amongst the higher groups. 
Summary of Results. 
I. All members of the Laminarieae possess an axile strand, 
in which are found numerous trump et-hyphae. 
II. In two genera only, Macrocystis and Nereocystis , are true 
sieve-tubes found in addition to trumpet-hyphae. 
III. In these two genera the trumpet-hyphae and the true 
sieve-tubes become in time obliterated by the development of 
callus on the sieve-plates in a manner comparable to the 
obliteration in the sieve-tubes of e. g. Cucurbita. 
IV. This callus is identical in all its micro-chemical re- 
actions with the callus of phanerogamic sieve-tubes, and may 
be regarded as chemically the same substance. 
V. The callus is formed by an alteration of the cell-wail in 
the trumpet-hyphae. 
VI. As a result of the investigation, Macrocystis and 
Nereocystis have been rightly very closely associated by 
systematists. 
Jodrell Laboratory, Kew. 
