POLLEN. 



99 



fingers (Anthyllis vulneraria) short 6-sided prisms with striated angles. A 

 cubical form obtains in the pollen-grains of Triopteris brachypteris and Basella 

 alba, that of a pentagonal dodecahedron in Banisteria, Rivima, and, in particular, 

 in a number of Caryophyllacese, e.g. Arenaria, Silene and Bianthus (cf. fig. 217 "). 

 In the Dandelion (Taraxacum officinale), and in Gorydalis lutea many crystalline 

 forms occur, side by side, in the same anther (cf. figs. 217 ^^ and 218*). The 

 tetrahedron, also, is not infrequently met with. This form occurs in Thesimn, 

 Cuphea, many Proteacete and Composites, sometimes with flat, sometimes with 

 curved surfaces (cf. fig. 218^). A form, made up as it were of two spherical 

 triangles joined together, occurs in Girccea and many other Onagracese (fig. 217 ^). 



The above paragraph relates solely to the varieties in form of dry pollen -grains. 

 In the great majority of cases the grains are variously striated and grooved. In 

 ellipsoidal and spherical grains, the grooves run like meridian-lines, so that two 



Fig. 218.— Pollen-grains. 



1 Nymphcea alba. 2 Viscum album. 8 Carlina acaulis. * Taraxacum officinale. * Cirsmm nemorale. ^ Buphthalmum 

 grandijlorum. ^ Bibiscus tematus. ^ Malva rotundifolia. ^ Campanula perswifolia; x200. 



poles are distinguishable. The number of the grooves is constant for a given 

 species, and even for whole families of plants. A single furrow is characteristic 

 of the grains of the Tulip-tree, Magnolias, and Water Lilies (fig. 218^), of the 

 Meadow Saffron, Tulip, Lily, Iris, Narcissus, and Snowdrop, of Palms, Grasses, and, 

 indeed, Monocotyledons generally. Two furrows are found on the pollen-grains of 

 Calycanthus, several climbing Smilacinese (Tamus, Dioscorea), and several species 

 of Amaryllis. A very great number of plants have three grooves, e.g. Eock-roses, 

 Violets, Poppies, Ranunculacese, Eoses, Almonds, many Papilionaceee, Beeches, Oaks, 

 and Willows, Solanacese, Gentians, Scrophulariaeeae, and many Composites 

 (cf. figs. 217^^ and 218^). Four grooves have been noticed in several Boraginese 

 (Anchusa, Nonnea), some Labiates (Teucrium Tnontanum, Sideritis scordioides), 

 in Houstonia, Platonia, Blachwellia and Gedrela odorata; six in most Labiates 

 (fig. 217^*), nine or ten in Sherardia, Borago, and Symphytum; twelve in 

 Grucianella latifolia; sixteen in Polygala chamcebuxus; twenty-one to twenty- 

 three in Polygala myrtifolia. On crystal-like pollen-grains the grooves are 

 extremely delicate, and their number depends on the number of angular ridges. 



