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K.—BOTANY. 187 
do the elaborated substances enter or leave the tubes, seeing that the 
whole system is self-contained ? 
3. Why are the tubes furnished with resistant internal thickenings ? 
Is it because their osmotic pressure is too low to resist the lateral pressure 
from the other medullary tissues ? If so, it is interesting to observe the 
evolution in this group of a device for strengthening the cellulose walls 
of (according to the majority of writers) proteid-conducting elements, 
subsequently elaborated in the higher plants for the strengthening of 
lignified water-conducting cells. 
4. Are the dilatations of any use to the plant, and is there any meaning 
in the frequent inequality of the two bulbs and their orientation? The 
possibility occurred to the writer that their peculiar form enabled the plant 
to utilise the tidal pressures to aid the translocation of substances within 
them. To test this, experiments were carried out on two different lines, 
but they had to be discontinued, partly because of the lack of time, but 
also because of the difficulty and expense of constructing a culture arrange- 
ment capable of standing alternating pressures of 20 ft. or more. The 
fact that some Laminarias grow round the edges of floating stages where 
there is no alternation of tidal pressure seems to make the hypothesis 
untenable ; still, it would be interesting to test it. 
There are numerous other details of cell structure in the Pheophycee 
that would repay investigation. Among them may be cited the 
strengthening bands of certain true sieve-tubes ; the fine striations across 
large cortical cell-walls (well shown, together with crossed pit-slits, in 
Chorda)” and in the long cells in the medulla of the stipe of Saccorhiza ; 
the complicated stratification of the very thick distal wall in 
the young antheridium of Dictyota with layers of different chemical 
composition, together with the sharply marked change in the nature of 
the vertical wall about midway between its base and apex, and numerous 
other interesting details. In the same genus, Heil® describes a swelling 
arrangement in the basal cell of the tetrasporangia that aids in the libera- 
tion of thespores. Thereis, as yet, no general agreement as to the supposed 
fusion of hyphe in the medulla of Laminariacee*®. Some cytological 
work of my own on the multinucleate cells of the meristematic region shows 
some interesting features. 
The great majority of Pheophycee are characterised by having long, 
delicate hyaline hairs which, in the higher forms, arise in clusters in 
so-called ‘ cryptostomata.’ It is a striking sight to see a miniature forest 
of Chorda in deep, clear water; each tall, thin plant surrounded by a 
widely-extending halo of pellucid hairs. In spite of all that has been 
written about these structures, their function remains conjectural. The 
following are some of the suggestions that have been made concerning 
their use :— 
(1) That they respire, and absorb nutritive substances. 
(2) That they serve as shock-absorbers and prevent injury to the plant 
from friction. 
(3) That they protect against intense illumination. 
* Pringsheim, E. G., Arch. Protistenk 47, 1924. 
8 Ber. d. Bot. Ges., 42, 1924. 
9 Killian, Zeitschrift fiir Bot., 1911. 
