The elements of botany for The elements of botany for beginners and for schools elementsbotany00gray Year: 1887 SECTION THALLOrriYTES. 171 set free is ready to f^erminate. Fig. 5G5 represents several stages of the conjugating process, wliicli, however, would never be found all togettier like this in one pair of threads. 513. Desmids and Diatomes, which are niicrosco])ic one-celled plants of the same class, conjugate in the same way, as is shown in a Closteriuni by Fig. 566, 567- Here the whole living contents of two individuals are in- corporated into one spore, for a fresh start. A reproduct
The elements of botany for The elements of botany for beginners and for schools elementsbotany00gray Year: 1887 SECTION THALLOrriYTES. 171 set free is ready to f^erminate. Fig. 5G5 represents several stages of the conjugating process, wliicli, however, would never be found all togettier like this in one pair of threads. 513. Desmids and Diatomes, which are niicrosco])ic one-celled plants of the same class, conjugate in the same way, as is shown in a Closteriuni by Fig. 566, 567- Here the whole living contents of two individuals are in- corporated into one spore, for a fresh start. A reproduction which costs the life of two individuals to make a single new one would be fatal to the species if there were not a provision for multiplication by the prompt divi- sion of the new-formed individual into two, and these again into two, and so on in geometrical ratio. And the costly process would be meaningless if there were not some real advantage in such a fresh start, that is, in sexes. 514. There are other Algae of the grass-green series which consist of single cells, but which by continued growth form plants of considerable size. Three kinds of these are represented in Fig. 568-571!. 515. Lichens, Latin Lichenes, are to be studied in the works of the late Professor Tuckerman, but a popular exposition is greatly needed. The subjoined illustrations (Fig- 575-580) may simply indicate what some of the commoner forms are like. The cup, or shield-shaped spot, or knob, which bears the fructification is named the Apothecium. This is mainly Fig. 568. Early stage of a species of Botrydium, a globose cell. 569, 570. Stages of growth. 571. Full-grown plant, extended aud ramified below in a root-like way. 572, A Vaucheria; single cell grown on into a much-branched tliread; the end of some branches enlarging, and the green contents in one (a) there condensed into a spore. 573. More magnified view of a, and the mature s})ore escaping. 574. Bryopsis phunosa; apex of a stem with its br
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