394 



BOTANY. 



diameter centrifugally, and the sheathing envelope of bark 

 centripetally, by the growth of new tissues between these 



two portions. 



Gymnosperms are all ter- 

 restrial, chlorophyll-bear- 

 ing plants ; none are 

 aquatic, and none are par- 

 asitic. Most of them are 

 large trees, a few only 

 being shrubs or under- 

 shrubs. 



506. — The flowers of 

 Gymnosperms are much 

 simpler than those of the 

 remaining Phanerogams. 

 They are always diclinous 

 -i.e., the male and fe- 



rig. 881.—^, a male flower of AWf '^f^dnrt- 

 ta ; 5, bracts ; a,stameiie. B. poUeu gmin ; ^, 



extine, with its large vesicnlar proirusions, i ■ j*js» 



U ; i, intine ; w, cell in the interior o! the pol- male Organs are in dltier- 

 len grain developing the pollen tube: j, banal x fl „,,,„,,„ 

 cellattacMng^ to the wall of the grain, s/ <mn em noweib. 

 — A after Sachs ; B after Schacht. 



J,. 300 ciiu iiuvTcii5. They consist 

 essentially of one or more 

 yariously shaped pollen-producing organs (stamens) on the 

 one hand, and naked ovules on the other ; both kinds of or- 

 gans are in most cases in structural connection with scale- 

 like'bodies, which serve as acces- 

 sory organs of reproduction. 



507. — The male flower in 

 Abies pectinata consists of an 

 elongated axis, upon which are 

 borne a large number of spirally 

 arranged stamens {a. Pig. 281, 

 A). Each stamen is morpholog- 

 ically a phyllome, which is here 

 modified into a body consisting 

 of a short stalk (filament) sup- 

 porting two pollen sacs (the an- 

 ther). The pollen grains are developed from mother-cells, 

 each of the latter giving rise to four grains. The pollen- 

 mother-cells themselves arise from the interior parenchyma 

 of the stamen by the differentiation and enlargement of cer- 



Fig. 282.— A catkin or spike of the 

 male flowers of Pinvs sylves' 

 Prom Le Maout and Decaisue. 



