148 DESCRIPTIVE BOTANY. PART 1. 



calyx (fig. 144.), or are perigynous (see art. 101.) ; 

 whilst in Polyandria they are free from the calyx, or 

 are hypogynous. 



The fourteenth and fifteenth classes are characterised 

 by a twofold consideration, the number and relative 

 lengths of the stamens. In Didynamia there are 

 four, and in Tetradynamia there are six ; but the 

 former is distinguished from Tetrandria, by two of the 

 stamens being always shorter than the other two ; and 

 he latter from Hexandria by two being shorter than 

 the other four. This is expressed by the word 8t>ya/xo< 

 (power), signifying that some of the stamens have an 

 ascendancy over others, and this is combhu'd with the 

 word which expresses their number. These circum- 

 stances are not always readily recognised by begin- 

 ners ; and they should take into consideration a few 

 other particulars which may enable them to correct 

 their judgment. Thus, in Didynamia, the four stamens 

 are not symmetrically disposed round the axis, but are 

 thrown together on one side of the flower, which is 

 always monopetalous * and never strictly regular. The 

 lipped flowers (Labiattp, art. 95. and fig. 93.) form a 

 large portion of this class, except- 

 ing a few of them, as the genus 

 Salvia, in which two stamens are 

 abortive, and which is there- 

 fore placed under Diandria. The 

 class Tetrandria is readily re- 

 cognisable, from the circumstance 

 of all its species having six sta- 

 mens, but only four petals, and 

 four sepals. It agrees precisely 

 with the natural order Crucifera?, 

 60 named from the petals being dis- 

 posed in such a manner as to re- 

 present a cross (fig. 145. a). (6) 

 shows the relative position of the floral organs. 



The names of the three next classes indicate that the 

 filaments are united into bundles, expressed by the 



