ORGANS OF REPRODUCTION. 



263 



Fig. 556. 



Fig. 554. Elliptical pollen of 

 Alilkwort (Po1>/gala) e. Ex- 

 tine. /. Slits Fig. 5.55. 



Tlie same pollen viewed 



from above Fig. .5.5G. 



Pollen-grain of Lactijn's 

 glomerata. After Juasieu. 



absent; but other botanists on the contrary, believe that the outer 

 membrane always exists, but that it is much thinner at these points 

 than elsewhere. In the greater number of Monocotyledonous 

 Plants, there is but one slit; while, on the contrary, three is a 

 common number in Dicotyledons. Sometimes there are six, 

 rarely four, still more rarely tAvo, and in some cases we find 

 twelve or more. These slits are generally straight, but in 

 Mimulus moschatns they are curved; and other still more com- 

 plex aiTangements occasionally occur. 



The pores like the slits, also vary as to their number. Thus 

 we commonly find one in Monocotyledons, as in the Grasses, and 

 three in Dicotyledons, Sometimes again, tlie pores are very 

 numerous, in Avhich case, they are either irregularly arranged, 

 or in a more or less regular manner. The pores, again, may be 

 simple, or provided with little lid-like processes whicli are 

 pushed otf at the period when the pollen-grains dehisce, as in 

 the Passion-flower {jig. 557, o, o, o), and Gourd {Jig. 558); hence 

 such pollen-grains have been termed operculate. 



Fig ■:. 



Fig 558. 



Fig. 559. 



Fig. 557^ Pollen of a Passion-flower (Passi.ttora). before burstin<'. o o o Lid- 

 like processes -— /''S- o-'^. Pollen of tlie Gourd, at the period of dehis- 

 cence, o, o. Lid-hke processes of the extine protruded by the projections 



t^ t, ot the intine. From Jussieu Fig. 5oif. Trigonal pollen of the 



Bvemng Primrose i^nothera biennis'). 



2. Contents of the Pollen-grains, or FouiUa. — The matter con- 

 tained within the membranes of the pollen-grains is called the 

 fovilla. It is a semifluid granular protoplasm in which are 

 suspended very small starch granules, and what appear to be 

 oil globules. As the pollen approaches to maturitv, the fovilla 



s 4 



