Pollen cell. In flowering plants the vegetative tube cell produces the pollen tube, and the generative cell divides to form the two sperm cells. Pollen is produced in the microsporangia in the male cone of a conifer or other gymnosperm or in the anthers of an angiosperm flower. Pollen grains come in a wide variety of shapes, sizes, and surface markings characteristic of the species (see electron micrograph, right). Pollen grains of pines, firs, and spruces are winged. The smallest pollen grain, that of the forget-me-not ("Myosotis" spp.), is around 6 µm (0.006 mm) in diameter. Wind-borne pollen grains can be
Fertilisation of Orchids for transferring pollen to insects. The first mechanism described is that of "Orchis mascula", which serves as an introduction to the explanation of other Orchidaceae. In the upper part of the flower a petal shelters the male organ which has two packages of pollen grains, held together by thin elastic threads. These pollen masses stand side by side and have stalks down to adhesive balls in a cup which keeps them moist and sticky. When an insect lands on the large projecting lower petal, the labellum, and pushes its head and proboscis into the centre of the flower and down