102 PART II. THE INTIMATE STRUCTURE OF PLANTS. [ 23. 



cells or ccenocytes (p. 94). The primordial reproductive cells of the Algae contain 

 chloroplastids (except spermatozoids of Characeae) : in the higher plants these 

 cells do not contain chloroplastids, but the oospheres contain leucoplastids 

 which become the plastids of the embryo and from which all the plastids of the 

 future plant are eventually developed. In the Alga?, likewise, whatever be the 

 form of the reproductive cell, a portion of it consists of hyaline kinoplasm (p. 95) ; 

 in the case of motile cells (zoospores, zoogonidia, planogametes, spermatozoids), 

 the anterior portion consists of hyaline colourless kinoplasm, whilst the thicker 

 posterior portion consists of granular cytoplasm containing the chloroplastids 

 when present ; similarly the oospheres of some heterogamous green Alga? (e.g. 

 (Edogonium, Vaucheria, Characeas), have an anterior region of hyaline kino- 

 plasm (commonly known as the receptive spot). In the higher plants the 

 spermatozoids consist exclusively of kinoplasm. The ccenocytic zoogonidium of 

 Vaucheria is peculiar in that it has no limited kinoplasmic area, but is entirely 

 covered by a layer of kinoplasm (see Fig. 75). 



Many of the primordial reproductive cells are motile (zoospores, zoogonidia, 

 plauogametes, spermatozoids), and move by means of cilia. A cilium is a deli- 

 cate filament of kinoplasm which is contractile, and by its oscillations serves to 

 propel through the water the body to which it belongs. The number of cilia 

 borne by these cells varies considerably: there may be a single cilium (e.fj. 

 zoospores of Botrydium, and occasionally those of Hydrodictyon) ; or a pair 

 (generally in plauogametes ; frequently in zoospores and zoogonidia ; less 

 commonly in spermatozoids, as those of most heterogamous Algae, of the 

 Bryophyta, and of Lycopodium and Selaginella) ; or four (e.g. zoogonidia of 

 certain green Algae, Ulothrix, Cladophora, Cha?tophora, Ulva) ; or many (e.g. 

 all motile cells of (Edogonium ; zoogouidia of Vaucheria ; spermatozoids of 

 Filicinae and Equisetinae). 



The position of the cilia is determined mainly by the distribution of the 

 kinoplasm : where, as in the ccenocytic zoogonidium of Vaucheria, there is a 

 continuous superficial layer of kinoplasm, the cilia are developed over the whole 

 surface ; where the kinoplasm forms the anterior end, the cilia are restricted 

 to this region ; when there are many cilia (e.g. (Edogonium), they form a 

 circlet round the base of the kinoplasmic area, and in the spermatozoids of the 

 Filicinae and Equisetinae, which consist entirely of kinoplasm, the numerous 

 cilia are borne laterally, generally near the apex, but sometimes (e.g. Marsilea) 

 at some distance behind it ; when there are one, two, or four cilia, they are 

 either apical (motile cells of most Green Algae, spermatozoids of Bryophyta, and 

 of Lycopodium and Selaginella), or they are borne laterally (e.g. spermatozoids 

 of Volvox and Vaucheria, among Green Alga? ; all motile reproductive cells of 

 the Brown Algae) at the base of the kinoplasmic area. 



Another peculiar feature of some of these motile primordial cells, is the 

 presence of an eye-spot. This is a small corpuscle of a red colour, consisting 

 apparently of a specialised mass of cytoplasm permeated by colouring-matter ; it 

 turns dark-blue on treatment with iodine. An eye-spot is present in the motile 

 cells of the isogamous Green Algae, in the zoogonidia of (Edcgonium, in the 

 spermatozoids of Volvox and Eudorina, and in all motile cells of the Brown Algaa. 



Yet another remarkable feature is the presence of a contractile vacuole, that 

 is, a vacuole in the cytoplasm which expands arid contracts rhythmically. These 



