. Botany for high schools and colleges. Botany. GYMNOSPEBM^. 395. tain cells. Each pollen grain is at first a single cell, but by the time it escapes from the anther it is a several-celled body, by the formation of partitions within its cav- ity (q, y, Fig. 281, B). The daughter-cells thus formed are doubtless the homologues of the prothallium of the higher Pteridophytes. Each mature grain has a double wall, of which the outer one (the extine) is hard and thick, while the inner one {in- ^^%^\^Ao1^. tine) is thin and °l Ptnw syiwstru ' showing the two pol- delicate (e and i, len Magnifie
. Botany for high schools and colleges. Botany. GYMNOSPEBM^. 395. tain cells. Each pollen grain is at first a single cell, but by the time it escapes from the anther it is a several-celled body, by the formation of partitions within its cav- ity (q, y, Fig. 281, B). The daughter-cells thus formed are doubtless the homologues of the prothallium of the higher Pteridophytes. Each mature grain has a double wall, of which the outer one (the extine) is hard and thick, while the inner one {in- ^^%^\^Ao1^. tine) is thin and °l Ptnw syiwstru ' showing the two pol- delicate (e and i, len Magnified., _,, .^v T- —FromLeMaoutand Fig. 281, B). In Decaisiie. this case (as indeed is common) there are two vesicular jjrotru- sions of the extine {bl. Fig. 281, B), which give the grain the ap- pearance externally of being three- celled. The of Pinus syl- vestris are collected into catkins Kg. ^, male flower of "i" ^pikcs (Fig. 282). They are Taxus baccata; a, th« pollen structurally similar to those de- sacs. 5, a stamen, seen from •* below. C, a piece of a foliage- shoot, s, with a leaf, b, in whose axil is a scaly axis (the fe- male flower), which is terminated by an ovule, sic; s, the scales. Z), longitudinal section of the fe- male nliwer in C more magnifled; scribed above. The stamens are short and broad, and each bears on its back or outer surface two elon- gated pollen sacs (Fig. 283). The L!Thf3y"or""nScieSs"TJhi PoUen grains are similar to those ovule; m, aril; ! rudimentary nf Ahi';i axillary ovule. (^T By an error ^"'ca. of the engraver the hair line from In TaXUS laccata the male flower a; IS carried about 1 mm. too high ., , , in the figure.) E, longitudinal differs from those described above section of an older ovule, but i • ji i p n before fertilization; j, integu- Only m the Shape 01 the stamens, S,Tpe?mTdra™%ho"l^4''tSe which are peltate and lobed (Fig. S"t'^Jfv'n^e'(^±2'piaTn:'ri
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1888
