POLLEN. 



99 



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

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

 alha, 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 1^). 

 In the Dandelion (Taraxacum officinale), and in Corydalis 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 Thesium, 

 Guphea, 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 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. 



L Nymphcea alba. ^ Viscum album, s Carlina acaulis. * Taraxacum o^cinale. ^ Cirsium tiem.orale. * Buphthalmivm 

 grandijlorum. 7 Hibiscus tematus. 8 Malva rotundifolia. 9 Campanula persicifolia ; x 200. 



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 Safiron, Tulip, Lily, Iris, Narcissus, and Snowdrop, of Palms, Grasses, and, 

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

 Galyeanthus, 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, Ranunculacese, Eoses, Almonds, many Papilionacese, Beeches, Oaks, 

 and WiUows, Solanacese, Gentians, Scrophulariaceae, and many Composites 

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

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

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

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

 Gruoianelia 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. 



