468 



BOTANY 



PART II 



spermatogenous cells (Fig. 415, A). By the further division of the central 

 cells, which represent a single antheridium, numerous spermatozoid mother-cells 

 are formed (B-JD). The periiiheral cells then break down and give rise to a 

 mucilaginous substance, in which is embedded the central mass of spermatozoid 

 mother-cells (E). The small prothallial cell (p), however, persists. The whole 

 male prothallium is up to this stage still enclosed by the wall of the microspore. 

 This ultimately ruptures, and the mother-cells are set free and liberate the club- 

 shaped spermatozoids. Each of these has two long cilia at its pointed end. 



The macrospores in some species similarly begin their development within 

 the sporangia. After the division of the nucleus — which lies in the peripheral 

 cytoplasm at the apex — into daughter-nuclei and their distribution in the apical 

 cytoplasm, the formation of cell walls begins. In this way, progressing from apex 

 to base, the spore becomes filled by a process of multicellular formation, with 



large prothallial cells. At 

 the same time, and proceeding 

 in the same direction, there 

 begins a further division of 

 these cells into smaller cells. 

 In some species the apical disc 

 of tissue is formed first, and is 

 separated by a thickened wall 

 or diaphragm from the rest of 

 the cavity of the spore ; cell- 

 formation occurs in this later. 

 In the tissue at the apex, con- 

 sisting of small cells, the rudi- 

 ments of a few archegonia 

 appear, often even before the 

 formation of the prothallium 

 has been completed. The 

 archegonia are usually not 

 formed until the spores have 

 been discharged from the spor- 

 angium. 



The wall of the spore 

 eventually bursts at the apex, and the prothallium becomes partially protruded ; 

 it forms a number of rhizoids on three projections of its tissue. The fertilisa- 

 tion of one or two archegonia, which then takes place, is followed directly by 

 the segmentation of the fertilised egg-cells and the formation of the embryos 

 (Fig. 416.) 



The embryogeny of Sela.fjinella recalls that of Lycoxiodium. The egg-cell is 

 divided by the formation of a transverse wall into two cells ; the upper and larger 

 cell increases considerably in size, and gives rise, by the division of its lower 

 portion, to a suspensor, while the lower cell, by repeated division, develops into 

 an embryo, the segmentation of which according to Bruchmann follows several 

 distinct types. While in S. Martensii, S. spimdosa, S. helvetica, and other 

 species the first rhizopliore comes between the suspensor and the foot (Fig. 417), it 

 arises in ,S'. J'oultcri and S. Kraussiana beneath the suspensor and foot, as it does 

 in Lyco2)odium. The stem apex, with the first pair of loaves, eventually grows 

 upwards, and the root also extends beyond the niacrospore. As the foot still 

 remains in the prothallium the young plant continues united to the s^wre, and 



Fig. 417. — Selaginella Martensii. Embryo before becoming 

 free from the prothallus in longitudinal section ; /, foot ; 

 ivt, rhizopbore ; et, suspensor ; k, cotyledons with tlieir 

 ligales. (x 150, after Bruchmann.) 



