rPTTRODTTCTION. 13 



morpJtosis or TTomoJofty (sometimes improperly called Morphology), the 

 consideration of wliich is liowever foreign to oiu' present purijose. 



To understand the arrangement of the floral parts, let us take a complete 

 flower, in which moreover all the parts avefree fi-om each other, definite in 

 number, i. e. always the same in the same sjjecies, and symmetrical or 

 isomeroiis, i. e. when each whorl consists of the same number of parts. 



Such a complete symmetrical ilower consists of either four or five whorls 

 of altered leaves placed immediately one within the other. 



The Calyx forms the outer whorl. Its parts are called sepals. 



The Corolla forms the next whorl. Its parts, called petals, usually al- 

 ternate with the sepals ; that is to say, the centre of each petal is imme- 

 diately over the interval between two sepals. 



The Stamens form one or two whorls within the petals. If two, those 

 of the outer whorl (the outer stamens) alternate with the petals, and are 

 consequently opposite to, or over the centre of the sepals ; those of the 

 inner whorl (the inner stamens) alternate with the outer ones, and are there- 

 fore opposite to the petals. If there is only one whorl of stamens, they most 

 frequently alternate with the petals ; but sometimes they are opposite the 

 petals and alternate with the sepals. 



The Pistils form the inner whorl, and usually alternate with the inner 

 row of stamens. 



In an axillary or lateral flower the upper parts of each whorl (sepals, petals, 

 stamens, or pistils) are those which are next to the main axis of the stem or 

 branch, the lower parts those which are furthest from it ; the intermediate 

 ones are said to be lateral. 



The number of parts in each whorl of a flower is expressed adjectively by 



the foUowmg nvimerals derived from the Greek : 



mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octo-, ennea-, deca-, etc., poly- 

 1-, 2-, 3-, 4-, 5-, 6-, 7; 8-, 9-, 10-, maui/. 



prefixed to a termination indicating the particular whorl referred to. 

 Thus, a Flo-wer is 



disepalous, trisepaloiis, tetrasepalous, polysepalous, etc., according as 

 there are two, three, four, or many sepals. 



dipetalous, tripetalous, tetrapetalous, polypetalous, etc., according as 

 there are two, three, four, or many petals. 



diandrous, triandrous, tetrandrous, polyandrous, etc., according as there 

 are two, tlu-ee, fom*, or many stamens. 



digynous, trigynous, tetragynous, polygynous, etc., according as there are 

 two, three, foui', or many pistils. 



And generally, if symmetrical, a flower is 



dimerous, trimerous, tetramerous, polymerous, according as there are 

 two, three, four, or many parts to each whorl. 



Flowers are unsymmetrical or anisomerotis, strictly speaking, when any one 

 of the whorls has a different number of parts from the other ; but when the 

 pistils alone are reduced in niunber, the flower is still frequently called sym- 

 metrical, or isomerous, if the calyx, corolla, and staminal whorls have all the 

 same number of parts. 



Flowers are irregular when the parts of any one of its whorls are imequal 

 in size, dissimilar in shape, or do not spread regularly round the axis at 

 equal distances. It is however more especially irregularity of the corolla that 

 is referred to in descriptions. A slight inequality in size or direction in the 

 other whorls does not prevent the flower being classed as regular, if the 

 coroUa is conspicuous and regular. 



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