210 OVl'LINES OF PLANT LIFE. 



When a great number of spore leaves are to be borne, the 

 torus is elongated, as in the mousetail (fig. 173); or greatly 

 enlarged, as in the strawberry (fig. 174); or transformed into 

 a cup, as in the rose (fig. 175). 



When flowers in large numbers are very closely associated, 

 as in the sunflower and its allies, the receptacles are joined 

 to form a large common receptacle. The receptacle in such 

 plants may be a cone, a dome, or a more or less flattened 

 disk. In the fig the common receptacle is pear-shaped, with 

 the edges almost meeting above and the flowers distributed 

 over the inner face of the fleshy sac (fig. 176). 



EXERCISE XLV. 



1. Bisect a flower of marsh marigold lengthwise. Observe the three 

 sorts of leaves, perianth, stamens, and carpels ; their relation to each 

 other and their insertion separately on the enlarged stem, the torus. 

 Separate some from an old flower and note the scars left by their fall. 



(T 278.) 



2. Are perianth leaves similar, or of two sorts ? (^ 293.) 



Dissect off a stamen. Observe the two parts : (a) the slender stalk, 

 filament, and (i) the enlarged part, anther. Note in the anther the two 

 lobes, each with a shallow groove marking the position of the two pairs 

 of spore cases. Tear open the spore case with a needle and observe the 

 innumerable pollen grains which they contain. Examine a naturally 

 bursted anther and determine how they open. (^^ 287-289.) 



Dissect off and examine a pistil. (H" 282.) Observe 



3. At the apex the roughened area, the stigma (T[ 283), sessile upon 



4. The enlarged part, the ovulary. Observe its flattened form and 

 the grooves along one edge. Split it along this line, flatten it out care- 

 fully and note the ovules attached to the edges. (If 286.) 



5 . Cut several transverse sections of the pistil and observe the thick- 

 ened edges of the carpel, forming the placenta, to which ovules are at- 

 tached. Compare sections. Are all ovules attached to same edge ? 



6. Study and compare the flowers of the sweet pea {Lathyrus odora- 

 tus), apple, fuchsia, and garden lily. 



