POLLEN. 



99 



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

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

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

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

 In the Dandelion {Taraxacihm officinale), and in Corydalis lutea many crystalline 

 forms 0CCU1-, side by side, in the same autlier {cf. figs. 217'- and 218^). 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®). A form, made up as it were of two spherical 

 triangles joined togethei', occurs in Circcea and many other Onagracese (fig. 217*). 



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

 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. 



■ NymphCBd alba. 2 Vi^cnm atbttm. 8 Carlina acanlis. * Taraxacum officinale. * CirsiuTn nejiwrale. 

 grandijloruin. ^ Bibiscus ternattis. ^ Maiva rotundifolia. ^ Campanula persiei/olui; x200. 



> Buphthalmum 



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. Rock-roses, 

 Violets, Poppies, RanunculacesB, Roses, Almonds, many Papihonacese, Beeches, Oaks, 

 and Willows, Solanacese, Gentians, Scrophulariacese, and many Composites 

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

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

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

 (fig. 217 "), 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. 



