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
Minuartia groenlandica it does flower anywhere between June to August. In this period pollen grains are transported from flower to flower by insects. The most effective insect to transport pollen grains is the bumblebee "Bombus terricola". This is due to tiny hairs on the bee that collect pollen, and the bee's habit of crawling all over the flower in low temperatures when it is too cold to fly. Greenland stitchwort is found in areas of high elevation where bedrock is exposed. The plant grows on rocky ledges and in fine gravel on slopes. The soil in this area has a pH of