236 STUDY OF COMMON PLANTS. 



Inflorescence. 



I. Observe first the cylindrical hollow stalk (scape) 

 by which the head is supported. How do those of older 

 specimens compare in length with those of younger ones? 

 Can you suggest any advantage in this ? 1 



II. The head is subtended by an involucre of green, 

 leaf-like bracts. 



1. Is there more than one row of bracts? How do the 



outer differ from the inner ones? 



2. Compare the position of the involucre in the early 



morning with that assumed later in the day, and 

 finally in the evening; in clear and rainy weather. 

 Do these observations suggest anything as to the 

 function of the involucre? 



III. Taking a well-developed head, not so old but that 

 a few of the flowers of the center are still unopened, make 

 a longitudinal section. 



1. Observe the disk-like, expanded end of the stalk on 



which the flowers are borne, the receptacle. Is it 

 concave or convex ? How does it compare in this 

 respect with the oldest receptacles from which the 

 seeds have fallen? Suggest advantages. 



2. Note the order of development of the flowers. Cen- 



tripetal or centrifugal ? 



Flowers. 



These should be studied in position and also separately, 

 removing for this purpose several flowers with a pair of 

 fine forceps. 



I. Examine a fully developed flower throughout. With 

 a good lens observe 



1 In this and some other cases it will be necessary to supplement the 

 laboratory exercises by out-of-door observations. 



