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7 
4 
3 
K.— BOTANY. 195 
From the Puget Sound Biological Station come a number of welcome 
investigations, by Gail, Shelford, and others, into such questions as the 
amount and nature of light penetration at different depths of the sea, 
the efficiency of light of different wave-length in photosynthesis at various 
depths, and the effect of the roughening of the surface in diminishing 
the light. It is interesting to get the zoning of the seaweeds correlated with 
exact data of light absorption as well as with percentages of exposure to 
the air. I believe that light affects marine plants in another way and one 
that is also fully deserving of investigation. The statements made by the 
writer regarding the periodicity of the sexual cells in Dictyota and its 
dependence on the local incidence of the spring tides have now been 
amply corroborated, and from widely separated localities. Hoyt®> does 
not accept the explanation that it is dependent upon the variation in 
the amount of light; but no one has-.as yet offered an alternative 
solution to the problem. Since then I have been able to study the 
question further, and my conviction that this is the correct solution 
is stronger than ever. (Incidentally, cannot some clever physicist find 
out for us why light is able in this particular case to produce such remark- 
able results, when it does not affect the tetraspores in the same plant, 
nor any of the three kinds of reproductive cells in Padina?) Now there 
are other ways in which these local differences in the time of spring tides 
may affect the plants. Compare two localities—one where low-water of 
spring tides always occurs about 6.0 in the morning and evening, whilein the 
other the times are at midnight and noon. In the case of summer-fruiting 
plants one would expect fruiting to be earlier under the former conditions; 
but in the case of winter-fruiting plants the results would be quite different. 
Take, again, the case of plants of half-tide level in a locality where low- 
_ water of spring tides occurs between 12.0 and 2.0. They are always 
emergent during the periods of intensest illumination. What will be the 
effect on the plants? The probability is that not only early or late 
fruiting, but also vigour of development, local distribution, especially 
of the smaller plants, and even the amount of epiphytic growth, will be 
_ affected. It would be interesting to collect data to test these hypotheses— 
4 
e 
they make the problem more complicated but also more interesting. 
Every marine algologist must have been puzzled by the distribution 
of some of the larger Brown Seaweeds. The rocky coasts inside Cardigan 
Bay have no Himanthala, Alaria, or Saccorhiza, and yet the surf on the 
_ Aberystwyth rocks is heavy enough. On the rocky promontories of Pem- 
_ broke and South Carnarvonshire to the north and to the south of 
_ the bay the plants are quite common. The explanation generally 
p 
ae 
given is that the plants demand pure water. Gail and Powers, both 
at Puget Sound, publish papers proving the importance of the H-ion 
concentration to the growth of marine plants, even of hardy ones 
like the Fuci. Gail makes the interesting statement that in the presence 
of much Ulva the P,, of the water is too high for Fucus. There may 
be another factor in operation. We know that certain substances essential 
to the welfare of the seaweeds—iodine, for instance—exist in the sea in 
very minute proportions, so that in order to obtain a sufficient supply 
the plants have to come in contact with an exceedingly great amount of 
continually moving water. Our young botanists would perform a great 
2 Johns Hopkins Univ. Circ., 195, 1907. 
02 
