. Morphology of spermatophytes. [Part I. Gymnosperms]. Gymnosperms; Plant morphology. CTCADALBS 19 III. THE GAMETOPHYTES. THE FEMALE GAMETOPHYTE The gametophyte generation begins with the reduction divi- sion of the enlarged mother cell which lies deeply imbedded in the nucellus and surrounded by more or less sporogenous tissue which does not function as such. According to Treub ^^ and Lang,^® in Ceratozamia and Stangeria the transverse division of the mother cell results in a row of three cells (Fig. 19), which may be called potential megaspores, the lowest of which becomes the functional meg
. Morphology of spermatophytes. [Part I. Gymnosperms]. Gymnosperms; Plant morphology. CTCADALBS 19 III. THE GAMETOPHYTES. THE FEMALE GAMETOPHYTE The gametophyte generation begins with the reduction divi- sion of the enlarged mother cell which lies deeply imbedded in the nucellus and surrounded by more or less sporogenous tissue which does not function as such. According to Treub ^^ and Lang,^® in Ceratozamia and Stangeria the transverse division of the mother cell results in a row of three cells (Fig. 19), which may be called potential megaspores, the lowest of which becomes the functional megaspore. Whether this is true of all Cycads or not remains to be seen. The selected megaspore enlarges rapidly at the expense of the two functionless megaspores, disorganizing them as well as a varying amount of adjacent tissue. The outer wall of the megaspore is said to become cu- tinized in Cycas, and this may be true of other genera as well. In any event, it suggests deriva- tion from forms in which the spores are discharged. The germination of the meg- aspore and the development of the female gametophyte was first published in any detail by Warming, *' ^ Cycas circinalis being the form studied. Addi- tional incidental testimony has been given by Treub," by Ikeno ^^ in his study of Cycas revoluta, and by Lang ^* in his study of Stangeria paradoxa. It is often stated in a general way that the development of the endosperm resembles that in Selaginella and Isoetes, but since our knowledge of the develop- ment in these forms has been obtained by putting together fragments of information, such a statement does not rep- resent any very exact knowledge. Unpublished results ob- tained by Miss F. M. Lyon with Selaginella show that some- thing more than inference from fragments is needed. So far Fio. 19.—Development of the megaspore: A, Stangeria paradoxa, showing the functional megaspore enlarging at the expense of two functionless mega- spores, X 250; JB, Ceratozamia longi- f
Size: 1815px × 1376px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorcoulterj, bookcentury1900, bookdecade1900, bookyear1901
