POLLEN. 



99 



fingers (Änthyllis 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, Rivina, and, in particular, 

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

 In the Dandelion (Taraxacum ojficinale), 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 Thesiutn, 

 CupJtea, many Proteacese and Composites, sometimes with flat, sometimes with 

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

 triangles j'oined together, occurs in Circcea 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 



7 vjT >" 



'WrU^' 



Fig. 218.— Pollen-grains. 



1 Nymphcea alba. 2 Viscum album, s Carlina acaulis. * Taraxacum oßcinale. s Cirsmm nemorale. « Btiphthalmum 

 grandißorum. ^ Hibiscus ternatus. ^ Malva rotundifolia. ^ Campanula persici/olia ; 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 Saftron, 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. Rock-roses, 

 Violets, Poppies, Ranunculaceas, Roses, Almonds, many Papilionacese, Beeches, Oaks, 

 and Willows, Solanacese, Gentians, Scrophulariacege, and many Composites 

 {cf figs. 217^^ and 218 2). Four grooves have been noticed in several Boraginese 

 {Anchusa, Nonnea), some Labiates {Teucrium montanum, Sideritis scordioides), 

 in Houstonia, Platonia, Blackwellia and Cedrela odorata; six in most Labiates 

 (fig. 217 1*), nine or ten in Sherardia, Borago, and Symphytum; twelve in 

 Crucianella latifolia; sixteen in Poly gala chamcabuxus ; 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. 



