1890-91.] A '■'■Colonial" Herbarium specimen. 471 



carps, mostly single, occur attached to the midribs of the ter- 

 minal segments, and on wart-like swellings of the " leaflets." 

 The carpospores, like the asexual tetraspores, are not endowed 

 with motion. 



Attached to the Delesseria at two points one can see small 

 specimens of Ulva — representatives of the great division of the 

 gi-een sea-weeds, such as have the chlorophyll unmixed with 

 red material. Ulva is a green strap-like sea^weed, tapering at 

 the base, where it is attached by a small disc to its support. 

 Propagation takes place by various methods. One is by 

 swarmspores — green round or oval bodies provided with 

 cilia, by which they are propelled through the water. Two 

 of them meet and fuse, the result being a body capable of 

 growing up into a new thallus. Another method is by zoo- 

 spores, which appear in specially modified cells of the thallus. 

 Lastly, certain cells resembling Protococcus or Palmella are 

 set free by degeneration of the tissues, and these either grow 

 directly into the normal thallus, or they develop zoospores 

 which produce the thallus. Minute examples of two other red 

 sea-weeds were discovered — viz., Plocamium and Polysiphonia 

 — into the life-history of which we need not enter. 



We now come to look at the organism for whose sake the 

 specimen had been kept. The individual examples of Isthmia 

 are, like other diatoms, very minute. It is possible to detect 

 them with the naked eye as mere shiny specks. Collectively 

 they form greenish tufts at the extremities of the branches of 

 the Delesseria. They attach themselves to this and to each 

 other by an exudation of mucus (protoplasm), which preserves 

 tenacity enough to enable the observer to lift them about in 

 bunches. Their outline and method of attachment are quite 

 characteristic, and familiar to microscopists. As is well 

 known to most naturalists, the framework of the diatom is of 

 silicic acid (flint), and it is very surprising to see how beauti- 

 fully geometric that structure is, and how faithfully a specific 

 pattern is followed. One is apt to forget, when viewing the 

 delicate markings of prepared diatoms under a high power, 

 that these are the outcome of vital influences at work in the 

 protoplasm of the plant, and not in any sense carvings, — a 

 notion which asserts itself very naturally. The mode of 

 propagation is peculiarly interesting. In construction the 



