Part 5 (1/2)

CHAPTER VI

THE BROWN ALGae (_Phaeophyceae_)

[Illustration: FIG 24--Forms of diatoms _A_, _Pinnularia_ i, seen froillaria_ (?) _C_, _Navicula_ _D_, _F_, _Eunotia_ _E_, _Gomphonema_ _G_, _Cocconeis_

_H_, _Diatoma_ All 300]

These plants are all characterized by the presence of a brown pigment, in addition to the chlorophyll, which al the plants a brownish color, ranging froht yellowish brown to nearly black One order of plants that possibly belongs here (_Diatole celled, but the others are for the e seaweeds The diatoms, which are placed in this class simply on account of the color, are probably not closely related to the other brown algae, but just where they should be placed is difficult to say In some respects they approach quite closely the desarded as related to the everywhere in stagnant and running water, both fresh and salt, fors on stones, le or united into filaments, and not infrequently are attached by25)

[Illustration: FIG 25--Diatoelatinous stalk

150]

They are at once distinguished from the desmids by their color, which is always some shade of yellowish or reddish brown The co 24, _C_), are boat-shaped when seen froreat variety in this respect

The cell wall is always ie amounts of flint, so that after the cell dies its shape is perfectly preserved, the flint lass These flinty shells exhibit wonderfully beautiful and delicate s which are sometimes so fine as to test the best lenses to make them out

This shell is co over the other like a pill box and its cover This arrange 24, _A_ ii)

Most of the diato over solid substances; but like the movements of _Oscillaria_ and the desh several explanations have been offered

They resemble somewhat the desmids in their reproduction

THE TRUE BROWN ALGae

These are all th in soood deal of differentiation in their tissues and organs

[Illustration: FIG 26--_A_, a branch of common rock weed (_Fucus_), one-half natural size _x_, end of a branch bearing conceptacles _B_, section through a conceptacle containing oogonia (_og_), 25 _C_, _E_, successive stages in the developonium, 150 _F_, _G_, antheridia In _G_, one of the antheridia has discharged the mass of spermatozoids (_an_), 150]

One of the commonest forms is the ordinary rock weed (_Fucus_), which covers the rocks of our northeastern coast with a heavy drapery for several feet above loater mark, so that the plants are completely exposed as the tide recedes The couished by the air sacs hich the stems are provided The plant is attached to the rock by s a steularly at intervals, so that the ultimate branches are very nuth of a metre or more The branches are flattened and leaf-like, the centre traversed by a thickenedbranches is occupied by a transversely elongated pit or depression The growing point is at the botto point the syht about Scattered over the surface are little circular pits through whose openings protrude bunches of fine hairs When wet the plant is flexible and leathery, but it , as may be seen when the plants are exposed to the sun at low tide

The air bladders are placed in pairs, for theit up to the surface when covered ater

The interior of the plant is very soft and gelatinous, while the outer part forh rind of26, _A_, _x_) are usually much swollen, and the surface covered with little elevations fro clusters of hairs like those arising froh one of these enlarged ends shows that each elevation corresponds to a cavity situated below it On soe-yellow mass; in others there are a nuh to be easily seen The yellow onia

If the plants are gathered while wet, and packed so as to prevent evaporation of the water, they will keep perfectly for several days, anddistances If they are to be studied away from the seashore, sections for microscopic examination should be ht of common salt to 100 of water) If fresh material is not to be had, dried specimens or alcoholic material will answer pretty well

To study the minute structure of the plant, make a thin cross-section, and mount in salt water The inner part or pith is coated cells, placed end to end, and fore spaces between filled with the inous substance derived froe is hard when dry, but swells up enorrow smaller and more compact toward the outside of the section, until there are no spaces of any size between those of the outside or rind The cells contain s to the presence of the brown pigment found in all of the class, in addition to the chlorophyll, they appear golden brown instead of green

No non-sexual reproductive bodies are known in the rock weeds, beyond sins of thenew plants In so_ _Ectocarpus_ and _La 28, _A_, _C_), zoospores are forans of the rock weed, as we have already seen, are borne in special cavities (conceptacles) in the enlarged ends of soured, _F vesiculosus_, the antheridia and oogonia are borne on separate plants; but in others, _eg_ _F platycarpus_, they are both in the sa 26, _B_) are coroard nu up the space within, and often extending out through the opening at the top

The reproductive bodies arise fro 26, _C_, _E_) arise as nearly colorless cells, that early become divided into two cells, a short basal cell or stalk and a larger teres rapidly, and its contents divide into eight parts The division is at first indicated by a division of the central portion, which includes the nucleus, and is colored brown, into two, four, and finally eight parts, after which walls are foronium is of a nearly uniforoniuht cells, still enclosed in a delicate27, _H_) Finally, the walls separating the inner cells of the oogoniu27, _I_) as naked balls of protoplasm, in which a central nucleus26, _F_, _G_) are s cells, at first colorless, but when ripe containing nu, reddish brown dots, each of which is part of a spermatozoid When ripe, the contents of the antheridiu the empty outer wall behind, but still surrounded by a thin membrane After a few minutes this membrane is dissolved, and the sper 27, _K_) are oval in for cilia attached to the side where the brown speck, seen while still within the antheridium, is conspicuous