Part 5 (2/2)

The act of fertilizationfresh antheridia into a drop of water containing recently discharged egg cells To obtain these, all that is necessary is to allow freshly gathered plants to remain in the air until they are soed fro as little drops, those with antheridia being orange-yellow; thethe oogonia into water, the egg cells may be seen to escape into the water, when some of the antheridia ed, and collect i cells, to which they apply the the ato the ss, it is impossible to see whether more than one spermatozoid penetrates it; but fro now secretes a wall about itself, and within a short tirow It beco attached to the parent plant or to sorows into the body of the young plant (Fig 27, _M_)

[Illustration: FIG 27--_H_, the eight egg cells still surrounded by the innerinto the water _J_, a single egg cell surrounded by spermatozoids _K_, mass of spermatozoids surrounded by the innerplant _r_, the roots

_K_, 300; _L_, 600; the others, 150]

The simpler brown seaweeds, so far as known, row directly into new plants, or, as has been observed in some species, two zoospores will first unite A few, like _Ectocarpus_ (Fig 28, _A_), are sie plants with complex tissues Of the latter, a familiar example is the common kelp, ”devil's apron” (_Lath, with a stout stalk, provided with root-like organs, by which it is firmly fastened Above, it expands into a broad, leaf-like frond, which in some species is divided into strips

Related to the kelps is the giant kelp of the Pacific (_Macrocystis_), which is said soth of three hundred metres

[Illustration: FIG 28--Foria (_sp_) _B_, a single sporangiuassum_) _D_, one-half natural size _E_, natural size _v_, air bladders _x_, conceptacle bearing branches]

The highest of the class are the gulf weeds (_Sargassum_), plants of the warmer seas, but one species of which is found fro 28, _D_, _E_) These plants possess distinct ste like berries, giving the plant a striking reseher land plants

CHAPTER VII

CLass III--THE RED ALGae (_Rhodophyceae_)

These are a dom, both on account of their beautiful colors and the exquisitely graceful forms exhibited by many of them Unfortunately for inland students they are, with few exceptions, confined to salt water, and consequently fresh h can be done with dried eneral appearance, and the fruiting plants can be readily preserved in strong alcohol Specimens, si placed in water will assued exposure, however, to the action of fresh water extracts the red pigment is found in the chlorophyll bodies, and usually quite conceals the chlorophyll, which, however, becoment is removed

The red seaweeds differ ree in the presence of the red pigment, and, at least in the main, in their reproduction The si like _Cladophora_; others for 30, _C_, _D_); while others, a which is the well-known Irish moss (_Chondrus_), form plants of considerable size, with pretty well differentiated tissues In such for a sort of rind; while the inner portions are er and looser cells, and may be called the pith Between these extrerow attached to rocks, shells, wood, or other plants, such as the kelps and even the larger red seaweeds They are most abundant in the warmer seas, but still a considerable nu into the Arctic regions

[Illustration: FIG 29--_A_, a red seaweed (_Callithamnion_), of the natural size _B_, a piece of the saes in the develop procarps _tr_ trichogyne iii, young; iv, ripe spore fruit I, III, 150 iv, 50 _E_, an antheridium, 150 _F_, spore fruit of _Polysiphonia_ The spores are here surrounded by a case, 50]

The methods of reproduction may be best illustrated by a specific example, and preferably one of the simpler ones, as these are most readily studied microscopically

The forrows attached to wharves, etc, beloatercoht rosy red, and with its graceful form and extreroup

If alcoholic material is used, it may be lycerine

The plant is co _Cladophora_ in structure, but with s 29, _B_) The non-sexual reproduction is by roups of four, are known as tetraspores In the species under consideration the mother cell of the tetraspores arises as a s 29, _C_ i) This bud rapidly increases in size, assu cut off fro 29, _C_ ii) The contents now divide into four equal parts, arranged like the quadrants of a sphere When ripe, the wall of the ives way, and the four spores escape into the water and give rise to new plants These spores, it will be noticed, differ in one iae, in being unprovided with cilia, and incapable of spontaneous movement

Occasionally in the same plant that bears tetraspores, but more coans, and subsequently the sporocarps, or fruits, developed from them The plants that bear them are usually stouter that the non-sexual ones, and the h to be readily seen with the naked eye

If a plant bearing ripe spores is selected, the young stages of the fe the younger parts of the plant The procarp arises frooes division by a series of longitudinal walls into a central cell and about four peripheral ones (Fig 29, _D_ i) One of the latter divides next into an upper and a lower cell, the fore known as a trichogyne (Fig 29, _D_, _tr_)

The antheridia (Fig 29, _E_) are hemispherical masses of closely set colorless cells, each of which develops a single spermatozoid which, like the tetraspores, is destitute of cilia, and is dependent upon the hborhood of the procarp Occasionally one of these speryne, and in this way fertilization is effected Curiously enough, neither the cell which is io any further change; but two of the other peripheral cells on opposite sides of the filaular29, _D_ III, IV)

While the plant here described roup, it must be borne in mind that many of them differ widely, not only in the structure of the plant body, but in the coans and spores as well The tetraspores are often imbedded in the tissues of the plant, or ed in the same way as here described, and the same is true of the carpospores These latter are in so 29, _F_), contained in urn-shaped receptacles, or they may be buried within the tissues of the plant

[Illustration: FIG 30--Marine red seaweeds _A_, _Dasya_ _B_, _Rhodyae attached) _C_, _Grinnellia_ _D_, _Delesseria_ _A_, _B_, natural size; the others reduced one-half]

The fresh-water forms are not common, butwater, attached to stones and ork, but are much inferior in size and beauty to the marine species The red color is not so pronounced, and they are, as a rule, somewhat dull colored