An introduction to the study of seaweeds / by George Murray.

  • Murray, George (George Robert Milne), 1858-
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: An introduction to the study of seaweeds / by George Murray. Source: Wellcome Collection.

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    reach so great a size as the marine, the former rarely attaining one third of a micro-millimetre in length, while some marine forms approach three micro- millimetres. They may be distinguished in the mass by their brownish colour. The infinitely varied markings on the siliceous valves afford systematic characters, and are fully displayed after cleaning—i.e. the removal of the organic matter by calcination, or by treatment with nitric acid. Owing to the silicified membranes, the plants when once formed are incap- able of further growth, though alterations of volume occur by the sliding of one valve over the other to the extent of the breadth of the girdle. It is impossible by mere verbal description to convey an adequate idea of the variety and beauty of the forms assumed by Diatoms, or of the fine sculpturing of their valves. In describing them it is the practice to denote the aspect in which the girdle side is presented as the girdle or zonal view, and the aspect which displays the surface of the valve as the valve view. When the latter is presented the central portion is fre- quently free from fine markings, and may be tra- versed longitudinally by a line called the suture or rapJie, while nodes or nodules representing thickenings occur at each end, or in the centre as well. Each Diatom contains a nucleus, and the colouring- matter occurs in plates or bands of more or less regular form; drops of oil are frequently also pre- sent. A resting condition sometimes occurs, in which pairs of new valves are formed within the original ones. Such states are called craticular states, and they appear to correspond to those con-