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, Rivina, and, in particular, 

 in a number of Caryophyllacese, e.g. Arenaria, Silene and Dianthus (cf. fig. 21 7 11 ). 

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

 forms occur, side by side, in the same anther (of. figs. 21 7 12 and 218 4 ). The 

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

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

 curved surfaces (cf. fig. 218 6 ). A form, made up as it were of two spherical 

 triangles joined together, occurs in Circcea and many other Onagraceaa (fig. 21 7 5 ). 



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. 



i Nyinphcea, alba, a Viscum adbum. Carlina acaulis. < Taraxacum ojjicinale. Cirsium nemoraU. Buphthalmum 

 grandiftorum. i Hibiscus tematus. 8 Malva rotundifolia. 9 Campanula persicifolia; 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 1 ), 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 Smilacineae (Tamus, Dioscorea), and several species 

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

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

 and Willows, Solanaceae, Gentians, Scrophulariacese, and many Composites 

 (cf. figs. 21 7 13 and 218 3 ). Four grooves have been noticed in several Boragineae 

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

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

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

 Crucianella 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. 



