394 



BOTANY. 



A 



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- 

 Fig. 281. 4, a male flower of AUe* wflna- ,-, i j t 



ta ; o, bracts; a, stamens. B, pollen grain ;e, I.e., tne male anu 16- 



extine, with its large vesicular protrusions, -, 



W , i, intine ; y, cell'in the interior of the pol- male Organs are in 

 len grain developing the pollen tube : q, basal . fl nwprc , TViPV 

 cell attaching j/ to the wall of the grain, x 300 ent novveife. ney 



-rafter sachs; B after Schacht. essentially of one or more 



variously 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, Fig. 281, 

 A). Each stamen is morpholog- 

 ically a phyllome, which is here 

 modified into a body consisting 



T , , ,, , ~; ... Fig. 282. A catkin or spike of the 



OI a Short Stalk (filament) SUp- male flowers of Pinus sylvestris. 



porting two pollen sacs (the an- From Le Maout K 

 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- 



