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2090 



A TEXTBOOK OF THEORETICAL BOTANY 



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in two whorls of three parts. The outer is calyx-hke while the inner 

 forms a corolla; or, in some instances, the outer whorl takes the form 

 of a corolla while the inner may be reduced to a minute size. The segments 

 may be free from one another or may be united in each whorl. Those 



of the outer whorl are usually imbricated and 

 the median segments of each whorl are different 

 in size, shape and often in colour from the 

 lateral ones, especially that of the inner whorl, 

 which is often much enlarged and modified to 

 form the lip or labellum. 



The whole perianth (Fig. 2027) is usually 

 twisted through 180'^' as a result of a torsion 

 produced by the ovary, so that the labellum is 

 placed in the anterior abaxial position. This is 

 called resupination. Moreover, the labellum 

 or more rarely the odd sepal may be prolonged 

 backwards into a spur or a sac which may either 

 collect nectar or itself function as a nectar- 

 secreting tissue. 



The androecium is composed of two 

 trimerous whorls of stamens, which are never 

 all present. There is usually either one or two 

 stamens, united to each other and to an exten- 

 sion of the gynoecium, which together form the 

 column (Fig. 2028). The anther or anthers 

 are bilocular and open introrsely by a longi- 

 tudinal slit. The pollen is granular and generally bound up by elastic 

 threads of viscin into two mealy or waxy masses called pollinia. At the 

 lower end the viscin is extended into a columnar organ, the caudicle. 



The gynoecium is composed of three carpels. The ovary is inferior 

 with three parietal placentas and one loculus or very rarely trilocular 

 with axile placentation. The stigma is generally much modified. In 

 Cypripediiim all three lobes are functional but more often the posterior 

 two only are functional, while the third is sterile and transformed into a 

 small pocket called the rostellum, which lies between the anther and the 

 functional stigmas. A portion of the rostellum is modified into a viscid 

 disc, the viscidium, to which the caudicles are attached. The ovules are 

 numerous and anatropous, and are exceedingly small. 



The fruit is a capsule which usually opens by from three to six longi- 

 tudinal slits. 



The seeds are very numerous and of microscopic size. They are often 

 elongated at each end or rarely possess wings and the testa itself is extremely 

 thin. At the time of shedding the embryo is undifferentiated, composed 

 only of a few cells and lies freely in the testa, there being no endosperm 

 present. 



The family is a large one containing at least 450 genera. They are world 



Fig. 2026. — Floral diagram 

 of Orchis masada. There 

 is one functional stamen in 

 the outer whorl and two 

 staminodes in the inner 

 whorl. The positions of 

 the missing stamens are 

 indicated by crosses. The 

 flower is represented in its 

 correct morphological re- 

 lation to the axis, i.e., be- 

 fore resupination. {After 

 Eichler.) 



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