362 



PLANT STUDIES 



Fit;. 323. 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 (Tig- 322). 

 By far the most common method 

 is for the wall of each sac to split 

 lengthwise (Fig. 323), which is 

 called longitudinal, dehiscence ; an- 

 other is for each sac to open by a 

 terminal pore (Fig. 322), in which 

 case it may be prolonged above into 

 a tube. 



241. 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. 324, A), and is dif- 

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

 which contains the 



ovules and is the a fill ^\[\ n 



real seed case, n \\ \|i| | j} 



known as t h e 

 ovarv; (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 Fig. 324. Types of pistils: .l, three simple pistils 



Surface for the TJol- (apocarpous), each showing ovary and style tipped 



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



len, the Stigma. showing ovary (/), separate styles (r/l, and stigmas 



111 other Cases ( "' ' (! ' a com P oun d pistil (syncarpous). showing 



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



Several carpels to- Bbrg and Schmidt. 



