AKGIOSPEEMS 323 



microsporophylls, and carpels or megasporophylls. The carpel 

 is also commonly called a pistil. A carpel is one megasporophyll 

 and a pistil may be one or several carpels joined together as 

 was shown in Chapters II and VII. 



The presence and nature of the floral structures and seeds 

 in this group and in the gymnosperms has, at various times, 

 given rise to different names for the division. Flowering plants 

 or seed plants are the most common names, and are good 

 names. Phanerogams, meaning "reproduction easily seen," was 

 applied when less was known of the intricacies of reproductive 

 processes. At that time pteridophytes, bryophytes, and thallo- 

 phytes were classed together as Cryptogams, meaning " repro- 

 duction difficult to see." These names are still used by many 

 people. An interchange of the names would better fit the facts. 



297. The stamen and microspores. In Chapter II, Sect. 21, 

 it was stated that the tip of the stamen is the anther. It is 

 borne by a slender stalk (the filament). In a transverse sec- 

 tion of an anther (Fig. 99) there appear the spaces in which 

 pollen grains (microspores) are formed. In a young anther 

 four spore-forming regions (sporangia) may be seen, but by 

 the time each sporangium has matured its spores, pairs of 

 sporangia have joined by the breaking down of the separating 

 walls. In a mature anther, therefore, but two pollen sacs are 

 present. Special arrangements exist for the opening or dehis- 

 cence of the anther (Fig. 100). The anthers may open length- 

 wise, by means of terminal pores, or in other ways. 



Since they are formed by division of cells, it is evident that 

 the pollen grains are asexual spores. When mature, each one 

 consists of a heavy outer wall, an inner wall, cytoplasm, and 

 nucleus. Often there are starch foods stored in the pollen grains. 

 Frequently pollen grains begin to germinate before they leave 

 the anther, so that two nuclei may be seen within the spore wall. 



The pollen grains must be placed upon the tip of the pis- 

 til before further development occurs. This process consti- 

 tutes pollination, to which a chapter has already been given 

 (Chapter VIII). 



