MORPHOLOGY OF HIGHER PLANTS. 375 



cases, the definition given it by some writers is very simple. It 

 is defined as a branch which bears sporophylls. As we have 

 seen, a sporophyll is a leaf which bears sporangia. According to 

 the definition given, the strobiles or cones of the Gymnosperms 

 and certain Pteridophytes, as the horsetails and club mosses, 

 are entitled to rank as flowers. In Angiosperms other leaves may 

 be present, and these are known as the FLORAL LEAVES. The 

 flower, then, in Angiosperms is made up of sporophylls which are 

 essential, and floral leaves which may or may not be present. But 

 in speaking of the sporophylls of the flower in Angiosperms it is 

 customary to use terms which were applied to them before their 

 relation to the similar organs in the Gymnosperms and Pterido- 

 phytes was understood. Thus the microsporophylls, as already 

 pointed out, are known as STAMENS,, and the megasporophylls as 



CARPELS. 



For a great many years botanists taught that the stamens and 

 carpels are transformed foliage leaves, in other words, that they 

 are derived from foliage leaves, but in more recent years the 

 view has been established that they arise as independent members, 

 are, in fact, as independent as the foliage leaves themselves. 

 Various transformations or modifications may and do occur, but 

 these are not confined to the foliage leaves alone, for under cer- 

 tain conditions the sporophylls may assume the character of floral 

 leaves. 



It is true that in the case of some ferns the sporophylls bear 

 a strong resemblance to foliage leaves, as in Dryopteris Filix-mas 

 (Fig. 53), but this does not necessarily prove that the sporophylls 

 of Angiosperms are transformed leaves, but only that the further 

 back we go, the less the degree of differentiation of parts until 

 we reach the unicellular alg?e. 



The flowers of the Angiosperms differ from those of the 

 Gymnosperms in that the ovules (megasporangia) are enclosed, 

 before pollination, in an ovary which has developed a special 

 organ the stigma for the reception of the pollen grains (micro- 

 spores), and the floral envelopes are much more conspicuous. 



The several parts of the flower are arranged more or less 

 compactly at the terminus of an axis known as the flower branch, 

 the special portion bearing these parts being known as the TORUS 



