140 STRUCTURE OF FLORAL ORGANS; FERTILIZATION 



reproduction can only be understood by means of a study ot 

 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 



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



of anthers may be learned 

 from Figs. 129, 130, and 152. 1 



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



largely upon the manner hi 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, 



, , i j j v 



the grasses, rushes, and sedges) 



FIG. 151. Cross section of anther 

 of mint 



d, groove along which the anther will 

 split open. Somewhat magnified. 

 After Bonnier and Sablon 



FIG. 152. Modes of discharging 

 pollen 



, by longitudinal slits in the an- 

 ther cells (amaryllis) ; B, by uplift- 

 ing valves (barberry) ; C, by a poro 

 at the top of each anther lobe (night- 

 shade). After Baillon 



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. 



