. Botany for agricultural students . Botany. HYDRODICTYON 309 Pediastrum. — A more complicated colony occurs in Pedi- astrum (Fig. 264), another form common in ponds and other quiet waters in warm weather. The cells, which are quite numerous in some species, form plate-like colonies in which marginal cells differ in form from those within. Both zoospores and gametes are produced in this form. Any cell may form zoospores, which escape from the mother cell enclosed in a membrane and then arrange themselves into a new colony. Instead of zoospores the cells may form gametes, which. Fig. 265. — Wat
. Botany for agricultural students . Botany. HYDRODICTYON 309 Pediastrum. — A more complicated colony occurs in Pedi- astrum (Fig. 264), another form common in ponds and other quiet waters in warm weather. The cells, which are quite numerous in some species, form plate-like colonies in which marginal cells differ in form from those within. Both zoospores and gametes are produced in this form. Any cell may form zoospores, which escape from the mother cell enclosed in a membrane and then arrange themselves into a new colony. Instead of zoospores the cells may form gametes, which. Fig. 265. — Water-net, Hydrodiclyon reticulatum. a, portion of a net (X about 2); 6, a cell which has formed zoospores; c, the zoospores formed into a small net within the mother cell; d, a cell in which gametes have fonned; at the left of the opening through which the gametes are escaping two gametes are shown fusing. resemble zoospores but are smaller and more numerous. The gametes, since they are alike, form zygospores, and each zygo- spore upon germination produces a new colony. Hydrodictyon. — This is the remarkable Water-net, in which the cylindrical colonies, often a yard or more in length, comprise thousands of cells so joined as to enclose polygonal meshes and thus form a net as Figure 265 shows. These massive colonies, buoyed up by bubbles of oxygen caught within them, often form extensive floating mats in lakes, ponds, and sluggish streams. New nets may arise from zoospores or from zygospores. When a cell reaches a certain size and other conditions are right, its protoplast divides into thousands of zoospores. These zoSspores do not escape but, after swimming about for a time in the mother. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Martin, John N. (John Nathan), b. 1875. New York : John Wiley & S
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
