72 PHjEOSPORE^l. 



L. digitata has a broad leaf, which, by the violence of the waves, is 

 torn into a number of palmate strips (Fig. 69). L. saccharina has 

 a small, undivided leaf. Alaria has a midrib and special fertile 

 fronds. A. esculenta occurs plentifully on the west coast of Nor- 

 way and on the shores of Great Britain. Chorda filum, a common 

 seaweed, is thick, unbranched, and attains a length of several 

 metres, without any strong demarcation between stalk and leaf. 

 Some attain quite a gigantic size, e.g. Macrocystis pyrifera, whose 

 thallus is said sometimes to be more than 300 metres in length. 

 The Lessonia-species, like the above, form submarine forests of 

 seaweed on the south and south-west coasts of South America, 

 the Cape, and other localities in the Southern Hemisphere. 



USES. The large Laminarias, where they occur in great numbers, are, like the 

 Fuel, used for various purposes, for example, in the production of iodine and 

 soda, and as an article of food (Laminaria saccharina, Alaria esculenta, etc). 

 Laminaria saccharina contains a large quantity of sugar (mannit) and is in 

 some districts used in the preparation of a kind of syrup ; in surgical operations 

 it is employed for the distension of apertures and passages, as for instance the 

 ear-passage. It is by reason of the anatomical peculiarities and structure of the 

 cell-walls, that they are employed for this purpose. The cell-walls are divided 

 into two layers, an inner one which has very little power of swelling, and an 

 outer one, well developed and almost gelatinous the so-called " intercellular 

 substance " which shrivels up when dried, but can absorb water and swell to 

 about five times its size. The stalks of Laminaria clustoni are officinal. 



Order 17. Cutleriacese. The thallus is formed by the union 

 of the originally free, band-shaped shoots. The growth is inter- 

 calary. Sexual reproduction by the conjugation of male and 

 female gametes. An asexual generation of different appearance, 

 which produces zoospores, arises from the germination of the 

 zygote. Gutleria, Zanardinia. 



Sub-Family 2. Acinetae. 



Branched, simple cell-rows with intercalary growth. The 

 organs of reproduction are partly uni- and partly multi-cellular j 

 in the unicellular ones a cell without cilia is formed, which may be 

 destitute of a cell- wall, but has one nucleus (oosphere ?), or which 

 has a cell-wall and contains several (generally four) nuclei 

 (aplanospores ?); in the multicellular, monosymmetric swarm-cells 

 with two cilia (spermatozoids ?) are formed. The fertilisation has 

 not been observed. 



Order 1. Tilopteridacese. Haplospora, Tilopteris. 



