110 CALIFORNIA FISH AND GAME. 
It follows that if a solution can enter into the cell, it would have 
first to pass through the protoplasm by way of the cell’s wall; but living 
protoplasm, unlike its walls, gives permeability to all substances in solu- 
tion in varying amounts, segregating certain cerystalloidal bodies from 
others, according to conditions. This power of decision is not entirely 
limited to the outer protoplastic covering or membrane. The vacuole’s 
wall has a similar distinction in its selective ability, and this selective 
power is so much greater than the osmotic pressures bearing on the 
cells that they often show great variation in chemical constituents and 
quantities to their surrounding medium. It seems remarkable that this 
medium containing three per cent of chloride of sodium, four one- 
hundredths of one per cent potash, and with the proportion of iodine 
so small that it requires more than 20,000,000 pounds of the sea water 
to furnish the kelp with one single pound of iodine, that we find that 
the cells of some of the plants select one and eight one-hundredths per 
cent potash, six-tenths of one per cent sodium, and three one-hundredths 
of one per cent iodine, in their fresh and natural state. These small 
ca 
@ 
2. 
a 
asd 
ae 
Fig. 58. Cross section of stem of kelp greatly enlarged, *« 400. Photograph by 
Edward FE. Porteous. 
elementary substances are large when compared to the quantity of 
metals the sea holds in solution, and upon which the seaweed has some 
absorptive power. In the ease of gold there is about one grain in every 
ton of sea water, yet kelp has been known to absorb twenty cents worth 
of this precious metal to the ton of green kelp. In the case of silver, 
there is about one grain to every six tons of sea water; but so far, except 
in the ease of Pocillopora alciconis, analyses have not shown silver in 
the plants. Of the lesser metals, no doubt traces may be found. How- 
ever, very little work has been expended in this direction. 
The rate of growth and the growing period, or seasonal growth, 
are still mooted questions. While it is believed that kelp grows all the 
time, it appears that there are periods when the growth is more luxu- 
riant. At least, this is borne out in the following observations. On 
bed No. 21, which undoubtedly has been cut over more than any single 
hed on the coast, and one which the writer has had under observation 
