46 PHARMACEUTICAL BOTANY 



vular openings. The pollen is usually a powdery substance which 

 shows under the microscope distinct grains of characteristic forms, sizes 

 and markings. Like starch grains, each represents a particular source, 

 hence the variety that may be examined is limited only by the number 

 of kinds of flowers available for the purpose. In order to study pollen 

 grains, take up by means of forceps a stamen whose anther is just de- 

 hiscing, or letting free its contents, and tap upon a sheet of white paper; 

 then examine with a Compound Microscope. 



The following are some of the forms of pollen grains: 



Four Spore Daughter cells hanging together as in the Cat Tail 

 forming a pollen grain. 



Elongated simple pollen grains as in Zostera. 



Dumb-bell shaped as the pollen of the Pines. 



Triangular, as in the Mexican Primrose. 



EcHiNATE. as in the Malvaceae. 



Spherical, as in Geranium. 



Lens shaped as in the Lily. 



The Gynoecium, or Pistil System. — The Carpel or megasporophyll 

 is the female organ of reproduction of flowering plants. In the Spruce, 

 Pine, etc., it consists of an open leaf or scale which bears but does not 

 enclose the ovules. In angiosperms it forms a closed sac which envelops 

 and protects the ovules, and when complete is composed of three parts, 

 the ovary or hollow portion at the base enclosing the ovules or rudimen- 

 tary seeds, the stigma or apical portion which receives the pollen grains, 

 and the style, or connective which unites these two. The last is non- 

 essential and when wanting the stigma is called sessile. The carpel 

 clearly shows its relations to the leaf, though greatly changed in form. 

 The lower portion of a leaf, when folded lengthwise with the margins 

 incurved, represents the ovary; the unfolded surface upon which the 

 ovules are borne is the placenta, a prolongation of the tip of the leaf, the 

 stigma, and the narrow intermediate portion, the style. A leaf thus 

 transformed into an ovule-bearing organ is called a carpel. The carpels 

 of the Columbine and Pea are made up of single carpels. In the latter 

 the young peas occupy a double row along one of the sutures (seams) of 

 the pod. This portion corresponds to the infolded edge of the leaf, and 

 the pod splits open along this line, called the ventral suture. 



Dehiscence, or the natural opening of the carpel to let free the con- 

 tained seeds, takes place also along the line which corresponds to the 

 mid-rib of the leaf, the dorsal suture. 



