154 ELEMENTARY STUDIES IN BOTANY 



For example, if the members of a flower are in sets of five 

 or four, the plant is a Dicotyledon ; if they are in sets of 

 three, the plant is a Monocotyledon. This distinction does 

 not hold in all cases, but it may be depended upon in the 

 majority of the ordinary flowers. 



It is very common for the stamen set to be doubled, so 

 that the flower of a Dicotyledon may have five sepals, five 

 petals, ten stamens, and five carpels; and the flower of a 

 Monocotyledon may have three sepals, three petals, six 

 stamens, and three carpels. On the other hand, in the most 

 advanced families of Dicotyledons the carpels become re- 

 duced in number. For example, in the most advanced family 

 of Angiosperms, and therefore the highest of all plants (the 

 family to which sunflowers, goldenrods, asters, dandelions, 

 etc., belong), the flower has five sepals, five petals, five 

 stamens, and two carpels. 



An important fact to notice is that all four members of a 

 flower may not have advanced together, so that some of the 

 members may have reached definite numbers, while the other 

 members still have indefinite numbers. For example, the 

 flower of the ordinary buttercup has five sepals and five 

 petals, but it has an indefinite number of stamens and carpels. 

 This is one of the facts that indicates that a buttercup is a 

 much more primitive flower than an aster. 



95. United petals. It is a very general tendency in 

 flowers for any set of members to develop altogether, and 

 thus appear as if they had been united. It should be em- 

 phasized that they are not united in the sense that they ever 

 were separate, but that developing all together, they appear 

 as if they had been united. There are all degrees of this 

 apparent union, from an appearance of union only at base 

 to an appearance of union throughout. 



It is so common for carpels to behave in this way, resulting 

 in " compound pistils," that it seems rather exceptional when 

 this is not the case (Fig. 110), Such behavior on the part 



