FERTILIZATION AND FRUIT-FORMATION IN CRYPTOGAMS. 



51 



size and form between ooplasts and spermatoplasts. The thallus in all species of 

 Fueu* is tough and leathery, brown in colour, foliaceous, and dichotomously branched 

 lobed, and has interspersed here and there air-containing swellings which serve 

 as floats. The apices of the lobes are punctate, and each spot corresponds to an 

 mternal cavity which has the form of a globular pit (see fig. 202')- Sectioas 

 through these cavi- 



t^^^f* 1 



ties show that a 

 large number of 

 segmented filaments 

 known as " para- 

 physes " spring 

 from the lining- 

 layer of the cavity. 

 In Fucus vesicu- 

 losus (figs. 202 and 

 203) these filaments 

 remain concealed in 

 the cavity; in some 

 other species of 

 Fucus they pro- 

 trude through the 

 narrow orifice (osti- 

 ole) of the cavity 

 in the form of a 

 pencil of hairs. 

 Amongst the fila- 

 ments other struc- 

 tures are also 

 formed within the 

 cavity. A few of 

 the cells lining the 

 cavity swell into 

 papillae, and each m s . 202. -FUCUS vesicuiosu,. 



i } i i i i Longitudinal section through one of the cavities in the thallus. - A vesicle surrounded by 



D y paraphyses from the bottom of the cavity. A detached vesicle containing eight 



the intercalation of ooplasts; the inner lamella swollen up. * Liberation of the ooplasts from a rent vesicle. 



(After TnurGt.) 



a transverse septum 



into two cells, one of which is spherical, whilst the other assumes the form of a 

 stalk bearing the upper one (see fig. 202 2 ). The protoplasm in the spherical cell is 

 dark brown, and breaks up into eight parts, which round themselves off and con- 

 stitute the ooplasts. The thick wall of the spherical cell resolves itself into two 

 layers, of which the inner one incloses the eight rounded protoplasmic bodies like 

 a bladder. This bladder stuffed full of ooplasts next detaches itself entirely, and 

 glides upward between the paraphyses until it reaches the orifice of the cavity. 



