. The microscope and its revelations. free-cell forma-tion is always connected, directly or indirectly, with a process ofreproduction rather than of growth, and takes two different forms,the one occurring in the production of the zoospores or ; swarm-spores of alga?, the other in the formation of pollen-grains, or of the endosperm withinthe embryo-sac of floweringplants. In the formercase, the endosperm, in-stead of dividing itself intotwo halves, usually breaksup into numerous segmentscorresponding with oneanother in size and form,each of which, escapingfrom the parent - cavity,becomes an ind
. The microscope and its revelations. free-cell forma-tion is always connected, directly or indirectly, with a process ofreproduction rather than of growth, and takes two different forms,the one occurring in the production of the zoospores or ; swarm-spores of alga?, the other in the formation of pollen-grains, or of the endosperm withinthe embryo-sac of floweringplants. In the formercase, the endosperm, in-stead of dividing itself intotwo halves, usually breaksup into numerous segmentscorresponding with oneanother in size and form,each of which, escapingfrom the parent - cavity,becomes an independentcell, without any investingcell-wall of cellulose, hencea primordial cell, en-dowed with a power ofrapid motion by means ofcilia or flagella. In thesecond case the endoplasnigroups itself, more or lesscompletely, round severalcentres, each of which hasits own nucleus, formed bysubdivision of the nucleusof the parent-cell; andthese secondary cells, invarious stages of develop-ment, lie free within thecavity of the PIG. 413.—Binary sithilirisian nf cclh in endo-sperm of seed of scarlet-runner: A, ordinarycell, with nucleus a, and nucleolus b, imbeddedin its protoplasm; B, cell showing subdivisionof nucleus into two halves, a and a; C, cell insame stage, showing contraction of endoplasni(produced by addition of wateri into two sepa-rate masses round the two segments of originalnucleus; D, two complete cells within mother-cell, divided by a partition. imbedded in its residual endoplasm, cadi proceeding to complete itself as a cell by theformation of a limiting wall of eellullose (fig 414). As a newgeneration in any phanerogamic plant has its origin in thefertilisation of a highly specialised germ-cell (contained AVI thintin- ovule) by the contents of a sperm-cell (the pollen-grain).so do we find, among all save the lowest cryptoyains, a provisionfor the union of the contents of two highly specialised germ-cells being fertilised by the access of mot
Size: 1454px × 1718px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
