224 



COMPENDIUM OF GENERAL BOTANY. 



assist in the expulsion of the pollen-grains when insects come in 

 contact with them. (See Fig. 152.) 



Let us now consider the anther in cross-section represented 

 considerably magnified in Fig. 153, A, B. A represents the 

 cross-section of an entire anther, in which the valves have separated 

 from the pillar (connective tissue) at z. B is the very highly mag- 

 nified portion /3 ; e is the epidermis and x the fibrous mechanical 

 layer. At $/, B, it can be plainly seen that the fibrous layer does 

 not extend quite to the pillar. Anatomically this is the weakest 

 point, and at which separation takes place. The middle portion 

 in A in which the vascular bundle lies is called the connective, 



FIG. 150. FIG. 152. 



FIG. 150. Anther of white lily. 



a and 6, Modes of dehiscence. (After Berthold and Landois.) 

 FlG. 151. Cross-section of an anther (After Berthold and Landois ) 

 FIG. 152. Longitudinal section through the pistil and two anthers of Calluna 



(After Berthold and Landois ) 



because it serves as a union between the two parts of the anther. 

 Each half may also possess two chambers ; the entire anther is 

 therefore either two- or /bw/'-chambered. If one supposes the 

 four chambers to be close together on one side of the connective 

 we have an anther with both longitudinal openings on one side. 

 If the dehiscence is inward (in reference to the ilower) the an- 

 thers are designated as being introrse ; if facing outward, they are 

 said to be extrorse. A teleological relation which has been studied 

 more in particular by JORDAN ' is of special importance. The 

 position of the nectaries is dependent upon introrsity and extrorsity, 



Die Stellung der Honigbebalter etc. Dissertation. Halle, 1886. 



