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
Parthenium hysterophorus production, an additive in manure for biogas production, as a biopesticide, and as green manure and compost. Contact with the plant causes dermatitis and respiratory malfunction in humans, and dermatitis in cattle and domestic animals. The main substance responsible is parthenin, which is dangerously toxic. It also is responsible for bitter milk disease in livestock when their fodder is polluted with "Parthenium" leaves. Among other allelopathic effects of the species, the presence of "Parthenium" pollen grains inhibits fruit set in tomato, brinjal, beans, and a number of other crop plants. Light infestations of "Parthenium hysterophorus" in cultivated fields may be