Xl] SHAPES OF POLLEN-GRAINS 93 



different plants. They are spherical or spheroidal in 

 the 



Juniper Hazel Hornbeam 



Elms Honeysuckle Spindle Tree, &c. 



Much more commonly they are more or less ellipsoid, 

 or oblong to fusiform, as in 



Oak Beech Willow 



Plane Bittersweet Ash 



Elder Aucuba Pear 



Gorse Sycamore Maple 



Holly Tamarisk Clematis 



Lime Horse-chestnut Vine 



Virginian Creeper Laburnum Rosacece, &c. 



More curious shapes occur in some plants, however, 

 such as the rounded-ellipsoid grains each with two flanking 

 air-vesicles, or balloons, found in Pines, Larch, &c. ; the 

 polyhedric grains of the Alder, the quadrangular pyramids 

 or prisms, or truncated cones of Ribes ; and even more 

 extraordinary shapes can be found. 



Another curious fact is the coexistence of more than 

 one shape in the same flower. This is well seen in the 

 Black Currant, where the grains may be shaped like a 

 tetragonal pyramid, or cone, truncate or not ; or a four- 

 angled prism, with the faces plane or curved ; or even 

 a globoid or deformed and creased body. No doubt some 

 of such polymorphic grains are imperfect, and the shape 

 varies (as does that of all pollen-grains) according as they 

 are viewed in water, or dry, or in some water-extracting 

 medium such as alcohol or glycerine ; but polymorphic 

 pollen-grains are known for many other plants, of which 

 I may mention the Rowan, and are very commonly found 

 of two sizes in different or in the same flowers, e.g. in the 

 Tamarisk. 



