. Plants and their uses; an introduction to botany. Botany; Botany, Economic. THE CLUB-MOriSES 547. Fig. 376.âMartiii'a Seluginella {SelaQinella Mariensii, Sclaginella PVniily, Sclagindlacew). Gerniiiiation of macrospore (»,"), cut vertically, showing the female gametophyte protruding from the ruptured .spore- wall (fipm) and exposing an unfertilized archegonium (ar), hut still enclosing two embryos {em}A, emb-) which have been pushed down into the nutritive prothallus {pr) by their suspensors {ct, et). (Pfeffer.)â Native home, Mexico; much cultivated. Fig. 377.âMartin's Selaginella. Emb
. Plants and their uses; an introduction to botany. Botany; Botany, Economic. THE CLUB-MOriSES 547. Fig. 376.âMartiii'a Seluginella {SelaQinella Mariensii, Sclaginella PVniily, Sclagindlacew). Gerniiiiation of macrospore (»,"), cut vertically, showing the female gametophyte protruding from the ruptured .spore- wall (fipm) and exposing an unfertilized archegonium (ar), hut still enclosing two embryos {em}A, emb-) which have been pushed down into the nutritive prothallus {pr) by their suspensors {ct, et). (Pfeffer.)â Native home, Mexico; much cultivated. Fig. 377.âMartin's Selaginella. Embryo (^}"), cut vertically to show its suspensor (et), root (w), leaves (hi, hi), ligules dig, Itg), and tip of stem (St). (Pfeffer.) projection dig) termed a ligide,^ arises, which, by secreting mucilage, serves to keep the tender terminal organs from drying. The formation of macrospores that begin to germinate while still within the sporangium, marks a most important advance in the care of offspring; for by this means not onlj^ are the chances of cross- fertilisation increased, but the embryo is afforded more protection, and the young plantlet can be provided with a larger quantity of promptly available food while preparing for independent life. Just one step further is needed as we shall sec, to attain the high develop- ment of parental care achieved by seed-plants. A similar differen- tiation of the sijores and sporangia into male and female is found also in certain types of Filicince, and in extinct Equisetina-. As with scouring-rushe,s and ferns, ,so with the club-moss class, the modern species but feebly represent their kin of the coal age. These include giant lycopods such as Lepido- dendron (Fig. 278, page 301) and Sigillaria (Fig. 277, page 299) wnth much-branched trunks ten meters or more in height and often a meter in thickness, bearing cones as large as those- of a pine tree, and forming extensive forests. â Lig'ule < L. lignla, a little Pleas
Size: 2295px × 1089px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1913
