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 ana 16- 



male organs are in differ- 



I. A, a male flower of Abie* pfcflnrt- 

 5, bracts ; a, stamens. B. pollen grain ; . 



-rafter Sachs; B after schacht. 



ent flowers. They consist 

 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 



Fig. 282. -A catkin or spike of the 



of a short Stalk (filament) SUp- male flowers of Plim* tylvtstris. 

 ,- 11 /, 1 From Le Maont and Decuiane. 



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- 



