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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    ever, been established by direct observation, is the fact that most of the Diatoms possessing such a power of movement possess also longitudinal sutures, and it is supported by the observation that fine particles of matter (not motile by themselves) sus- pended in the water, on coming in contact with the membrane, are set in motion along the suture. However, no one has so far demonstrated the pro- trusion of any protoplasm at this place. That these movements take place with considerable relative force is shown by the observation of Donkin, who saw one species push away another at least six times its size, while other observers state that they have seen this greatly exceeded. The speed of the move- ment when compared with the rapid dartings of ciliated organisms is slow. The Rev. William Smith estimated the rate at about four hundred times a Diatom's length in three minutes. Reproduction.—Diatoms multiply by successive bi- partitions. The actively vegetating cell increases slightly in volume, and the two valves are slowly pushed out until the overlapping girdle remains in that position, but no more. The protoplasm then divides into two, and two daughter-cells are formed, not separated by a membrane in the ordinary way, but each new cell forms a new valve on the plane of division. The edges of the new valves fit into the girdle of the old valves of the parent cell, and these old valves overlap the new ones. Each daughter- cell thus possesses two valves, one newly formed and overlapped by the old one. The cells either separate and become free, or they remain in contact, and