Primary callose

Deposition of the matrix substances and formation of the microfibrils are accompanied by a sequence of related processes that lead to the development and differentiation of the cell wall this sequence includes expansion of the wall, changes in the composition of the polysaccharides, organization and orientation of the different layers, deposition of callose for formation of pores in phloem, lignification (see p. 299), and other processes. Considerable information has been obtained about the mechanism of some of these processes and the factors that affect them this information has been reviewed by leading molecular biologists, and will very briefly be mentioned here because of its relevance to cell-wall formation and to the constitution of cell-wall polysaccharides of interest to carbohydrate chemists. According to the new concepts, the transformations of the cell wall are effected, or are assisted, by the presence of a variety of enzymes, proteins, and, perhaps, even ribonucleic acid to the extent that primary... 

The whole pectin fraction usually contains one or both types of pectinic acid and arabinogalactans. Hemicellulose is a complex mixture of arabino-galactan, xylans, sometimes some glucomannan or galactoglucomannan, and callose. Its composition is variable with the source. The cellulose fraction, not only contains p-l,4-glucan, but almost always has small amounts of inseparable glucomannan. The primary cell wall is relatively richer in hemicellulose than the secondary wall, while the latter contains a good deal of cellulose. Pectins are found in primary walls and probably comprise much of the middle lamella. 

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