143 



great groups. Thus we find that the male and female 

 sporophylls of phanerogams are called stamens and carpels 

 respectively. The sporophylls with the portion of the shoot 

 on which they are borne constitute the flower, while in many 

 cases other leaves surround the sporophylls and form a perianth. 

 The microsporangia are the pollen-sacs., the macrosporangia, 

 the ovules. The microspores are the pollen grains, the 

 macrospore is the embryo-sac ; both kinds of spores containing 

 as usual a single nucleus, the division of this nucleus in each 

 case is the first step towards the formation of a prothal- 

 lium (i.e. the oophyte). The male prothallium is always 

 minute and consists of only a few cells, the most noticeable 

 portion of it being the so-called pollen-tube. Spermatozoids 

 are rarely formed and are usually represented by two small, 

 naked, nucleated, male cells which travel down the pollen 

 tube and eventually pass out at the apex. The cells arising 

 from the repeated nuclear division in the macrospore consti- 

 tute the female prothallium, which is sometimes large and 

 forms the tissue known as endosperm. In the prothallium 

 an oosphere arises, either as a naked cell, or in an arche- 

 gonium. Fertilisation is accomplished with the fusion of the 

 nucleus of a small male cell with that of the oosphere ; while, 

 from the resulting oospore, the embryo, or young sporophyte, 

 is produced. Here then the prothallium never has an in- 

 dependent existence apart from the spore which has pro- 

 duced it. The female prothallium remains altogether inside 

 the macrospore, the latter remains inside the macrospo- 

 rangium, and the latter remains for a long time attached to 

 the parent plant or sporophyte. Eventually the whole 

 macrosporangium with the macrospore and contained embryo 

 separates from the parent plant as the seed. Thus the 

 oophyte does not form a distinct and separate stage in the 

 life history. The embryo during its growth and development 

 frequently absorbs the rest of the tissue formed in the 

 macrosporangium and consequently the kernel of the ripe seed 

 consists of the embryo alone. In such cases the seed is said 

 to be eocalbuminous. In other cases some of the tissue of the 

 macrosporangium persists in the ripe seed and the latter is 

 said to be albuminous. Such persistent tissue is distinguished as 

 endosperm, or perisperm, according as it has developed within, 

 or without, the macrospore. See also p. 58. Phanerogams 

 are divided into the two following main divisions : 

 I. Gymnosperms. 

 II. Angiosperms. 



