140 STRUCTURE OF FLORAL ORGANS; FERTILIZATION 



FIG. 151. Cross section of anther 

 of mint 



reproduction can only be understood by means of a study of 

 certain forms in the fern group, or pteridophytes ; for these 



structures had their origin in 

 connection with the develop- 

 ment, from simpler conditions 

 among the fern group, of the 

 habit of producing seeds. The 

 subject is treated at some 

 length in Part II, Chapters 

 xxvi to xxx inclusive. 

 173. The anther and its 



s, pollen sacs, with grains of pollen; contents. Some of the shapes 

 d, groove along which the anther will ,1 i i 



split open. Somewhat magnified. - of anthers may be learned 



After Bonnier and Sablon from FigS. 129, 130, and 152. 1 



The shape of the anther and the way in which it opens depend 

 largely upon the manner in which the pollen is to be discharged 

 and how it is carried from flower to flower. The commonest 

 method is that in which the 

 anther cells split lengthwise, as 

 in Fig. 152, A. A few anthers 

 open by trapdoor-like valves, as 

 in B, and a larger number by 

 little holes at the top, as in C. 



The pollen in many plants 

 with inconspicuous flowers (as 

 the evergreen cone-bearing trees, 

 the grasses, rushes, and sedges) 

 is a fine, dry powder. In plants 

 with showy flowers it is often 

 somewhat sticky or pasty. The 

 forms of pollen grains are ex- 

 tremely various. Fig. 153 will serve to furnish examples of 

 some of the shapes which the grains assume ; c in that figure 

 is perhaps as common a form as any. Each pollen grain 

 1 See Kerner and Oliver, Natural History of Plants, Vol. II, pp. 86-95. 



FIG. 152. Modes of discharging 

 pollen 



A, by longitudinal slits in the an- 

 ther cells (amaryllis) ; B, by uplift- 

 ing valves (barberry) ; (7, by a pore 

 at the top of each anther lobe (night- 

 shade) . After Baillon 



