. Text-book of botany, morphological and physiological. Botany. ZYGOSPORES. tf3 creep about in troops, come into close contact with one another, and finally coalesce into large lumps. As soon as one of these lumps is formed, the rest collect from all sides round it as a centre, coalesce with it, and increase in this manner the mass of protoplasm which then becomes more and more rounded off. There is every reason to believe that this collective union of zoogonidia is a conjugation and therefore a sexual act, in the same sense as the conjugation of the zoogonidia of the Pando- rineae; and the la
. Text-book of botany, morphological and physiological. Botany. ZYGOSPORES. tf3 creep about in troops, come into close contact with one another, and finally coalesce into large lumps. As soon as one of these lumps is formed, the rest collect from all sides round it as a centre, coalesce with it, and increase in this manner the mass of protoplasm which then becomes more and more rounded off. There is every reason to believe that this collective union of zoogonidia is a conjugation and therefore a sexual act, in the same sense as the conjugation of the zoogonidia of the Pando- rineae; and the large mass of protoplasm formed in this way, which is called a Plasmo- dium, must therefore be treated as the analogue of the zygospore. The only difference is that in this case the zygospore does not become invested with a cell-wall nor go through a period of rest, but at once undergoes further development, becoming transformed into a stalked fructification which produces a large number of spores. In accordance with their mode of origin these spores may be compared not merely with the zoospores developed from the zygospore of Pandorina, but also with the ascopores of the Ascomycetes, and even with the spores of the Muscineae. The formation of this fructification out of the roundish Plasmodium of Dictyostelium com- mences with the production in its centre by free cell-formation of a number of cells each surrounded by a cell-wall of cellulose, which unite into a parenchymatous tissue forming in the interior of the Plasmo- dium a column or stalk standing erect on the substratum. As this column con- tinues to grow in height, the rest of the protoplasm which surrounds it creeps up it, and collects at its summit into a round lump, the entire substance of which now breaks up into a number of spores. This example furnishes the simplest case of the course of devel©p- ment of a Myxomycete. In most other instances it is much more complicated, the development being more complete, and a red
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1882
