Pollination cones (female), but some species are monoecious and others dioecious. A pollen cone contains hundreds of microsporangia carried on (or borne on) reproductive structures called sporophylls. Spore mother cells in the microsporangia divide by meiosis to form haploid microspores that develop further by two mitotic divisions into immature male gametophytes (pollen grains). The four resulting cells consist of a large tube cell that forms the pollen tube, a generative cell that will produce two sperm by mitosis, and two prothallial cells that degenerate. These cells comprise a very reduced microgametophyte, that is contained within the resistant wall of the pollen
Enteric coating However, as the solvents for such solutions are organic solvents, there's a concern about the toxicity potential of the traces of the residual solvents in the tablet coating. The first form of gastro-resistant coating was introduced by Unna in 1884 in the form of keratin-coated pills, although it was later discovered that they weren't able to withstand gastric digestion. Salol was also used by Ceppi as one of the first forms of enteric coating. However, the first material that was extensively used as enteric coating agent was shellac, since its introduction in 1930. Properly treated or hydrolyzed shellac showed different