158 THE STRUCTURE OF FLOWERS. 



The influence of the environment upon the anatomical 

 and morphological structures of plants has been lately and 

 widely studied from several points of view ; and it has been 

 shown conclusively, by Constatin and others, how a change of 

 medium — as, for example, from air to a subtei-ranean one, or, 

 again, to water — profoundly affects every tissue of the plant, 

 whether the root, stem, or leaves be submitted to it. So, too, 

 leaves of many plants have been proved to be very sensitive 

 to changes of position and to different amounts of light — 

 which is a most potent and exciting cause in affecting the 

 mesophyl, palisade, and other tissues, including the epider- 

 mis, stomata, and even cuticle. It is foreign to my purpose 

 to describe or discuss these details in the vegetative system 

 of plants ; my sole object being to draw attention to the fact, 

 and then to apply it to the sti'ucture of flowers. 



Irritability of the Floral Organs. — Perhaps no parts of 

 plants are more keenly sensitive to stimuli, or show a greater 

 number and variety of results to excitement than flowers. 

 A large proportion resemble plants which sleep, i.e. they 

 exhibit movements ac(!ording to the amount of light and heat 

 which they receive. So various is this, that LinnoBUS was 

 able to frame his floral clock. While many thus open their 

 petals at definite periods and subsequently close them and 

 die, as Convolvulus ; yet a large number reopen them again 

 when the due amount of light returns, like Daisies and 

 other Composites, AnagalKs arvensis, MesemhryantTiemimi, etc. 

 Others, like Silene nutans, unroll their petals at night, but 

 roll them up again by day.* Besides these spontaneous 

 motions of the perianth, the stamens often exhibit move- 

 ments, apparently without any external stimulus. Thus 

 Parnassia and Saxifrages slowly move their stamens in suc- 



* See Dr. Kerner's description of this flower. Flowers and their 

 Unbidden Guests, p. 133. 



