SPERMATOPIIYTES : ANGIOSPEKMS 



199 



FIG. 168. Cross - section of 

 anther of a lily (Butomus), 

 showing the separating walls 

 between the members of each 

 pair of sporangia broken 

 down at z, forming a con- 

 tinuous cavity (pollen sac) 

 which opens by a longitudi- 

 nal slit. After SACHS. 



The opening of the pollen-sac to discharge its pollen- 

 grains (microspores) is called dehiscence, which means "a 

 splitting open," and the methods of 

 dehiscence are various (Fig. 167$). 

 By far the most common method 

 is for the wall of each sac to split 

 lengthwise (Fig. 168), which is 

 called longitudinal dehiscence; an- 

 other is for each sac to open by a 

 terminal pore (Fig. 1670), in which 

 case it may be prolonged above into 

 a tube. 



111. Megasporophylls. These 

 are the so-called " carpels " of Seed- 

 plants, and in Angiosperms they 

 are organized in various ways, but 

 always so as to inclose the mega- 

 sporangia (ovules). In the simplest 



cases each carpel is independent (Fig. 169, A), and is dif- 

 ferentiated into three regions : (1) a hollow bulbous base, 



which contains the 

 ovules and is the 

 real seed case, 

 known as the 

 ovary ; (2) sur- 

 mounting this is a 

 slender more or less 

 elongated process, 

 the style; and (3) 

 usually at or near 

 the apex of the style 

 a special receptive 

 surface for the pol- 

 len, the stigma. 



In other cases 

 several carpels to- 



FIG. 169. Types of pistils : A, three simple pistils 

 (apocarpous), each showing ovary and style tipped 

 with stigma ; B, a compound pistil (syncarpous), 

 showing ovary (/), separate styles (g), and stigmas 

 (n) ; C, a compound pistil (syncarpous). showing 

 ovary (f), single style (g), and stigma (n). After 

 BERG and SCHMIDT. 



