peesideist's addeess. 131 



like manner the pinks and purples range over all those charm- 

 ing colours yielded by modern anniline dyes, lavender, lilac, 

 heliotrope, -claret, majenta, and crimson. These form a glorious 

 group. 



Most, if not all the whites ; several blues, and some few from 

 the other colour groups, are opaque, but by far the larger num- 

 ber of those coloured are transparent. Hence, sometimes reflected 

 light must be used as well as transmitted light ; indeed, both should 

 be always used, as the first best reveals external characters, and 

 the latter internal structure and composition as well as colour. 



Second, those that owe their colour to some physical condi- 

 tion. Most of this class belong truly to the colourless group, 

 others to the pale blues, and a few to some of the other groups. 

 The conditions are, first, the presence of fine strias on the Extine, 

 which act as a grating and resolve the white light into its con- 

 stituent coloured rays, yielding therefore exquisite prismatic 

 colours, as in Lycopersicum, where the Extine is very finely 

 and symmetrically scratched on each facet ; second, varying 

 thickenings of the Extine by very thin successive laminte, and 

 so refraction does what refiection did by the striae, viz., decom- 

 pose the white light, as in Alopecuris agrestis, where the flattened 

 sides covered by successive parallel layers yield a beautiful play 

 of complementary colours ; third, by varying densities in the 

 parts of the pollen which causes the grains to present two col- 

 ours, again generally complementary, as in Anthjllis vulneraria, 

 where the two large eyes of the pearly white oblongs are laven- 

 der, whilst the edges of the muff are pale green. Epilolium 

 angustifoUum shows pale green ground with pink hairs ; Linaria 

 cymhalaria, pearly white ground with delicate mauve margin ; 

 Princes-Eeather (Amaranthus) shows three discs with large cir- 

 cular craters of a yellowish-brown on a pale green field. Others, 

 though more distinctly modified by the presence of colouring 

 matter and by degrees of transparency, present most charming 

 pictures, as Armeria vulgaris^ cells yellow, teeth red ; Cypripe- 

 dium insigne, yellow ground crossed longitudinally by pale brown 

 bands ; Calla Ethiopica^ pearly white with brown nucleus ; Ifar^ 

 cissus poeticus, dark nucleus on bright yellow field. 



