THE ANGIOSPERMAE 



1085 



Fig. 1055. — Tiilipa sylvestris. An 

 actinomorphic, monocotyledo- 

 nous flower. All the parts of 

 the perianth are petaloid. 



be formed by the modification of other parts, i.e., stamens, petals or sepals 

 or of portions of these organs. 



When both stamens and carpels are present the flower is said to be 

 hermaphrodite. If the individual flowers contain only stamens or carpels, 

 but both types of flowers are present on 

 the same plant, the condition is described 

 as monoecious; while if staminate and 

 carpellate flowers are separated on difl^erent 

 plants, it is described as dioecious. When 

 all the parts of the flower are uniformly 

 developed and arranged around a common 

 centre the flower is said to be radiallv 

 symmetrical or actinomorphic (Fig. 1055). 

 If however the parts are unequally deve- 

 loped or arranged so as to create a bilateral 

 symmetry, the flower is called zygomor- 

 phic, the single plane of symmetry, along 

 which the flower may be divided into two 

 equal halves, being usually vertical, that is 

 to say in line with the inflorescence axis 

 and the bract of the flower. 



Viewed in vertical section, the arrange- 

 ment of the parts, in which the carpels 

 stand highest, i.e., superior, is described as hypogynous. In a number 

 of families, however, the receptacle appears to be expanded laterally, 

 so that the perianth and stamens stand away from the carpels, on the 

 edge of a disc, or hollow cup, which raises them to the level of the carpels 

 or even above them. Such flow^ers are called perigynous. Finally this 

 cup-shaped structure may completely enclose the carpels, which then 

 appear to be embedded within a solid covering of tissue and to lie below the 

 level of the other flower parts. The flower is then epigynous and is said to 

 have an inferior ovary. 



It is a common error of speech to refer to flowers as if they w^ere sexual 

 structures and to speak of the stamens as male and the carpels as female 

 organs. While it is true that the flow^er serves the function of sexual repro- 

 duction, it is itself a purely sporophytic structure and its reproductive 

 parts are sporangia. The pollen-sacs are micro-sporangia and the pollen 

 grains are microspores. The ovules are not themselves strictly comparable 

 to megasporangia, but they each enclose a megasporangium, containing 

 megaspores. The gametophytic generation is represented only by extremely 

 reduced vestiges, little more than the gametes themselves, which are 

 produced enclosed within their respective spores. That the production 

 and operation of the gametes are thus hidden within the organization of 

 the flower, naturally accounts for the confusion above referred to, 

 against which, how^ever, the mind of the botanist should be carefully 

 guarded. So long as the true conditions are properly understood there 



