BOTANY. 



375 



•case or box, usually double, opening at a cer- 

 tain period on eiich side, and scattering an 

 excepilingly fine powder, called the -pollrn. 

 The forms of the anther ai-e various, and like- 

 wise the modes of opening. (See figure 

 2.) Thus sometimes, and indeed most fre- 

 quently, the opening is by a longitudinal slit 

 the whole lengtli of die anther ; in many in- 



Fig 



stances it is a small pore or pei-foratioii at the 

 extremity, and in others it tukes place by a 

 little door or valve turning upward, as shown 

 in our figures. 



The grains of pollen arc very beautiful ob- 

 jects for the microscope, tinder which they 

 present a gi-e'at diversity in size, fonn, und 

 structure. (See tig. 3.) 



GRAINS OF POLLEN MAGNIFIED. 



The pollen is an agent of vast importance in 

 the economy of the vegetable kingdom ; the 

 maturity of fruit and the production of seed 

 being dependent upon the contact of these 

 minute bodies with the stigma or summit of 

 the pistil. About the period at which the 

 anthers burst and scatter the pollen, the sur- 

 face of the stigma is seen to be moistened by 

 a viscid, secretion, that, occasioning the ad- 



Fi 



herence of such grains as light upon it at tno 

 moment of dispersion, so acts likewise upon 

 them as to stimulate the ejection of one or 

 more slender tubes from the surface of each 

 individually ; which tubes e.xtending more 

 or less according to the length of the pistil, 

 penetrate through its tissue until they reach 

 the interior of the germen and come in con- 

 tact with the embiyon seeds. In the event 

 .4. 



POLLEN TUBES. 



of this contact not taking place, the seed be- 1 oidy two or three perfect seeds, instead of 

 comes abortive ; and hence in many seed- nine or ten, perhaps, whose rudiments were 

 cases, as those in the common pea, we find ' present. The grains of pollen, examined by 

 (759; 



