94 The Flora of Wiltshire. 



generates the dust, which, carried from the bush by winds, gives 

 rise to the minute fungus which is the cause of the rust in wheat. 

 This opinion is groundless, for the rust in corn is occasioned by 

 the growth of " Puccinia graminis" (Pers.) a very different plant 

 from that which grows on the leaves of the barberry. There is 

 however another parasite still more common on the leaves of this 

 shrub than the "JEridium," and that is the " Erysiphe pcnicellata," 

 (Schlecht) or Barberry Mildew. This frequently covers the whole 

 surface of the leaves with a thin white substance, which, when ex- 

 amined with a microscope, appears to consist of very delicate forked 

 filaments, with very minute dark coloured globular bodies inter- 

 spersed amongst them. Whether this has any influence in causing 

 the mildew in corn growing in its neighbourhood, Cryptogamic 

 Botanists are as yet undecided. 



The barberry affords a good example of leaves acquiring the con- 

 dition of spines from their parenchyma being absorbed, and the 

 ribs becoming indurated, and afterwards in their axil spring up 

 leaves of the ordinary kind. The flowers yellow, in elegant droop- 

 ing racemes, consist of three sets of floral envelopes, (which are 

 modified leaves, 1 ) containing six stamens highly curious in their 

 formation opposite the petals 2 which surround a single pistil. 

 When first expanded the stamens are inclined back upon the petals ; 

 on the filaments being touched near their base, they immediately 

 start forward towards the pistil so that the anther is brought into 

 contact with the stigma. If the anther be fully matured it is burst 

 by the violence of the motion, and the pollen projected on the stig- 

 ma. The stamens after a short time resume their original position, 

 and may be again stimulated. If we examine more minutely this 

 beautiful contrivance, it will be found that the stamen is capable 

 of moving towards the pistil by a hinge-like motion, and that the 

 filament is endowed with an exquisite irritability, so that it is 



1 The idea that the leaf is the type of all the floral organs, originated with 

 Linnseus. A clearer enunciation of tbis theory, and a fuller development of the 

 whole were made by Goethe. 



• Tbis is an apparent exception to the truth of that general and important law 

 of the alternate disposition of vegetable organs. A more detailed account of 

 this beautiful arrangement, will be given in the order Primulacece. 



