116 



PART II. THE INTIMATE STRUCTURE OF PLANTS. 



[26. 



ceeds in essentially the same manner as that of the zoogonidium described 

 above. In the Characese, where the spermatozoid still retains some zoogonidial 

 characteis, the hyaline pointed anterior portion, bearing a pair of cilia, is de- 

 veloped from the kinoplasra ; the thick posterior portion, which is highly granu- 

 lar, is developed from the nutritive hyaloplasm of the cell; the nucleus lies 

 centrally at the junction of the two portions. In the Bryophyta and in the 

 Pteridophyta the spermatozoid consists simply of kinoplasm with a nucleus ; it 

 contains no nutritive cyto-hyaloplasm, and so differs essentially from a zoogon- 

 idium. In these two groups of plants the mature spermatozoid consists of an 

 anterior kinoplasmic poition bearing the cilia, and a posterior portion consisting 



of the e^ngated and 

 curved nucleus invested by 

 a thin layer of kinoplasm. 

 In the Pteridophyta the 

 posterior nuclear portion 

 of the spermatozoid more 

 or less completely sur- 

 rounds a mass of nutritive 

 cyto-hya'oplapm which re- 

 mains attached to the 

 ppermatozoid in the form 

 of a vesicle for a short 

 time after extrusion from 

 the antheridium, becoming 

 eventually disorganised. 



The non-motile male 

 cell (spermatium) of the 

 Eed Algffi is developed 

 singly in a mother-cell, 

 and appears to consist 

 merely of a small mass of 

 kinoplasm with a nucleus. 

 Oospheres are, as a rule, 

 developed singly in the 

 female organ, though 

 there are some exceptions 

 (see p. 82) : their develop- 

 ment has not yet been so 

 minutely studied as has 

 simplest case, as in the 



FJO. 75. Development of the crenocytic zoogonidium of 

 Vaucheria sessilis. A-E Stages in the development of 

 the zoogonidium within the gonidangium ( x 95) ; F ti 

 free zoogonidium (x 20/) ; G a portion of F more highly 

 magnified (x 450) showing the hyaline superficial la.yer 

 bearing the pairs of cilia, with a nucleus opposite the 

 point of origin of each pair. (Alter Strasburger.) 



that of zoogonidia and spermatczoids. In the 

 oogonium of (Edogoninm, the cytoplasmic contents of the oogonium con- 

 tract away from the cell-wail and round themselves into a spherical form ; 

 at one side a colourless hyaliue area is differentiated, the receptive spot, the 

 rest of the oosphere containing chloroplastids, etc. This hyaline receptive 

 spot corresponds to that in the zoogonidium of the same plant, as also to the 

 hyaline anterior portion of the spermatozi-ids already described ; it is doubtless 

 developed in the same way, and consists of kinoplasm. At this stage the 

 oogonium opens by the rupture of the cell-wall, and a portion of the hyaline 



