210 OPENING OF THE PASSAGE TO THE INTERIOR OF THE FLOWER. 



expression " Opening of Flowers " in the headline above, since flowers exist to which 

 the term " open " does not apply. The flowers of the Snapdragon and Toadflax 

 {Antirrhinum and Linaria) never open spontaneously ; but the insects which frequent 

 them for honey have to open the door for themselves by pushing down the lower 

 lip. So, also, in the flowers of Papilionacese. In the bud the uppermost petal or 

 standard incloses the four others like a mantle; only when the pollen is mature, and 

 has been discharged from the anthers, does the standard fold back, and one says 

 the plant is in flower. But still no opening is to be seen, access to the honey remains 

 now, as before, hidden, and insects must introduce their probosces between the 

 folded petals. Still, from a consideration of these and other cases, it may be urged 

 that there is essentially an opening of what was closed in the bud, a giving of access 

 to the interior of the flower, so that perhaps the headline above meets the case. 



The arrangement of the petals in the flower-bud is determinate for individual 

 cases, and is often made use of by descriptive botanists as a useful character for 

 discriminating families and genera. This manner of folding is known as ^Estivation, 

 of which several forms are distinguished. (1) The crumpled aestivation, character- 

 istic of the Poppy, Cistus, and Pomegranate (Papaver, Cistus, and Punica). The 

 petals here, to quote Grew, " are cramb'd up within the Empalement [i.e. calyx] by 

 hundreds of little Wrinkles or Puckers; as if Three or Four fine Cambrick Hanh- 

 cherchifs were thrust into ones Pocket ". (2) Plaited or plicate aestivation, where 

 a funnel- or bell-shaped corolla is folded in regular, longitudinal pleats, as in Venus's 

 Looking-glass (Specularia). (3) When the band-like corollas of many Composites, 

 as the Salsify and Dandelion {Tragopogon and Taraxacum) are rolled up longi- 

 tudinally into a tube closed above by five little teeth, one speaks of a convolute 

 aestivation; (4) when, as in Umbelliferse and many Caryophyllaceae, the petals are 

 rolled up from apex to base, of a circinate aestivation. (5) Sometimes the folded 

 or unfolded petals are so placed one upon the other, that on one side each is in 

 contact with the adjacent petal of that side, and on the other side with that of the 

 other, the whole corolla appearing spirally twisted. This condition is known as 

 contorted aestivation, of which examples are the Wood-sorrel (Oxalis), Periwinkle 

 {Vinca), and other Apocynaceae, Solanaceae, and Convolvulaceae. (6) The commonest 

 form of aestivation is that in which the petals or lobes of a united corolla overlap 

 like tiles on a roof, without being twisted, however. The outmost petal covers all 

 the rest, or a pair of outer petals inclose a pair of inner ones. This, the imbricatr 

 aestivation, is characteristic of the Apple, Rose, Buttercup, and Anemone, also, in a 

 modified form, of Papilionaceae and Pinks. (7) In a number of plants, e.g. Asarum, 

 Lilac, and Vine, the petals do not overlap, but touch merely by their margins, and 

 form a sort of dome or vault. This is known as valvate aestivation. Among these 

 kinds of aestivation vai'ious combinations occur, thus the Poppy in addition to beinf,^ 

 crumpled is imbricate, and several Pinks (Dianthus neglectus, glacialis, &c.) with 

 imbricating petals are also convolute. It further often happens that the leaves of the 

 calyx have an aestivation difiering from that of the corolla. Here, again, the Poppy 

 is an instance in point, its calyx is valvate, and its corolla imbricate and crumpled. 



