560 



HUTCHINSON'S POPULAR BOTANY 



other seaweeds have also been used as food, chiefly by the maritime 

 peasantry and fisher-folk. 



Speaking of the fertilization of Polysiphonia subulata, which belongs 

 to this class, Professor McAlpine says : " It is evident that the element 

 of chance enters largely into the meeting of the passive male and female 

 elements, and it is not to be wondered at that in many cases fertilization 

 never takes place at all. Professor Dodel-Port has, however, recently 

 observed that Infusoria create currents in the water and thus set the passive 

 sperm-cells [spermatia] in motion. Numerous Vorticellae, or Bell-animal- 

 cules, attach themselves to this seaweed, and create currents which send 

 the sperm-cells spinning about, while the forked hairs beside the trichogyne 

 help to break the force of the current and cause the sperm-cells to settle 

 there. Just as insects obtain pollen or honey from a flower while un- 

 conscious agents in its fertilization, so do these water-animals swallow 

 some of the sperm-cells for their pains. Contrivances in Flowerless Plants 

 for ensuring fertilization may not be less wonderful, when better known, 

 than those brought to light in Flowering Plants " (fig. 705). 



The PH^EOPHYCE^, or 

 Brown and Olive Sea- 

 weeds, include the Wracks 

 and Tangs, which are abun- 

 dant and conspicuous on 

 the rocky coasts of the 

 colder seas (figs. 701, 702, 

 714). Here, again, there is 

 great diversity of form, size, 

 and structure, which may 

 be well exemplified by a 

 comparison of the thread- 

 like rows of simple cells in 

 Ectocarpus with the broad 

 leathery fronds of Lami- 

 naria and Alaria on our 

 own coasts, the Antarctic 

 Macrocystis, with floating 

 ribbons two or three hun- 

 dred yards long, and the 

 tree-like Lessonia of the 

 same regions. Reproduc- 

 tion of the Brown Algae 

 varies in the several orders. 

 Photo [E - step - There are asexual swarm- 



FIG. 707. PEACOCK s- TAIL (Padina pavorna). . . , 



spores produced in large 



A much-prized Seaweed of sandy shores. The light zones bear . 



lime crystals. numbers and discharged 



