354 TEXTBOOK OF BOTANY 



constitute the corolla. The calyx and corolla together are often called the 

 floral envelope or perianth. The next two whorls of organs are less leaf- 

 like in appearance and each consists of three stamens. The stamens in 

 one cycle alternate with the sepals; those in the other cycle alternate 

 with the petals. Each stamen has a stalk or filament terminating in a 

 pollen-bearing anther. The pistil is centrally located in the flower and is 

 composed of three leaf-like parts, the carpels. The slightly thicker lower 

 portion of the pistil is the omilary,^ which tapers apically into a neck-like 

 structure, the style, at the summit of which is the three-lobed stigma. 

 Each lobe of the stigma is in line with the midrib of a carpel. 



If the ovulary is cut or broken crosswise the ovules from which seeds 

 develop may be seen. If the carpels are pulled apart lengthwise, the six 

 vertical rows of ovules are easily seen. As the pistil enlarges and becomes 

 a fruit, the ovules become seeds. 



The foregoing is a description of the usual tulip flower. Variations may 

 be found, some of which are inherent in the variety of tulip, while others 

 are the result of the conditions in which the bulbs are stored during their 

 dormant period. 



The calyx of the pea flower (Fig. 153) like that of bean is green, and 

 the four or five sepals are united except at their tips which may appear 

 as large teeth or calyx lobes. The corolla is variously colored and is com- 

 posed of five petals, so unique in form that special terms have been ap- 

 plied to them. One, the "standard," is broad and encloses the others in 

 the bud; the two lateral petals are "wings"; and the remaining two are 

 more or less united ventrally, forming the "keel" and enclosing the 

 stamens and pistil. Of the ten stamens, one is free; but the filaments of 

 the other nine are united in a tube surrounding the pistil. 



The pistil of the pea or bean consists of a single carpel but usually 

 contains several ovules attached to a longitudinal ridge at one side of 

 the ovulary. The region to which an ovule is attached is called a placenta. 

 The leaf-like nature of the carpel is clearer when a green pea pod is 

 opened along one side and spread out flat. If a cross section of the pod 

 is made, the ovules appear to be borne on the fused margins of a folded 



leaf. 



The stamens, petals, and sepals of such flowers as the tulip develop 



1 The ovulary of the pistil is often referred to as an ovary. The term ovary is used to 

 designate a very different sort of structure in animals. Later on we shall see that the 

 origin of egg-bearing structures in plants is quite unlike that of the ovule-bearing struc- 

 tures. It seems preferable, therefore, to use the term ovulary to refer to the ovule-bearing 

 structure in plants. 



