5$ FIRST GROUP. THALLOPHYTES. 



through a broad fissure in the two outer layers (IV), and remains for a time as a thin- 

 walled spherical body considerably larger than the zygospore itself. In it may be seen 

 (V) imbedded in fatty protoplasm two chlorophyll-masses, which were distin- 

 guishable in the zygospore. The contents now contract and surround themselves with 

 anew cell-wall (V), from which the former wall separates as a delicate vesicle. After a 

 time the protoplasmic body becomes constricted in the middle, and separates into two 

 hemispheres, each of which contains one of the two chlorophyll-bodies (VI). Each 

 hemisphere is at first without a cell-wall and is again constricted ; but this time the 

 constriction does not reach to the middle, while the hemisphere changes its shape in 

 other respects, and each finally appears as a symmetrically lobed cosmarium-cell ( VII), 

 which now assumes a proper cell- wall. The planes of the constrictions of both the 

 cells cut the planes of division of the germ-cell produced from the zygospore at 

 a right angle, and they are themselves also at right angles to one another ; the two cells 

 therefore lie across one another in the mother-cell. In each of them the contents 

 arrange themselves in the manner above described ; the wall of the mother-cell is 

 absorbed, and the cells separate. All these proceedings are completed in from one to 

 two days. The young cells, whose cell-wall is smooth on the outside, now divide in 

 the usual manner, but the new lobes that are added are larger and rough on the 

 outside ( VIII, IX, X}. The four daughter-cells of the two cells produced in germination 

 are therefore of two different forms ; two of them have equal, two unequal lobes ; the 

 latter yield always in division a cell with equal and a cell with unequal lobes, the 

 former only cells with unequal lobes. 



CHAEACEAE. 



The Characeae l occupy the highest place among the green Algae, and are not 

 very closely allied to any of them. Their very complex structure gives them the 

 appearance of small Cormophytes ; their organs of fertilisation also show peculiarities of 

 form and an amount of differentiation which we have not hitherto met with. Thread-like 

 motile spermatozoids are formed in very peculiar antheridia (globules), and the oogonium 

 is invested before fertilisation with five spirally twisted tubes, which spring from 

 its pedicel-cell. The whole organ thus formed, that is, the oosphere with its envelop- 

 ing tubes and the pedicel-cell, is termed the oogonium (nucule). The oosphere by fertili- 

 sation becomes a resting spore with a thick cell-wall, and in germination developes a 

 pro-embryo, on which the sexual plant arises as a lateral shoot. Gonidia (swarm- 

 spores &c.") are wanting, as they are in many species of Vaucheria and in the 

 Conjugatae. 



The Characeae are submerged water-plants, which are rooted in the ground and 

 grow erect, attaining a height of one-tenth of a metre to a metre, and are rich in 

 chlorophyll ; their growth is slim, for the stems and leaves are not more than from one- 

 half to two millimetres in thickness, and their structure is delicate, being strengthened 

 sometimes by a deposit of lime on the surface of the plants. They are social plants and 

 form close patches at the bottom of fresh-water and brackish lakes, ditches and streams ; 

 some grow in deep water, some in shallow, some in stagnant water and some in rapid 

 streams ; perennial species grow intermixed with annual. 



1 A. Braun, Ueber die Richtungsverhaltnisse der Saftstrome in den Zellen der Charen (Monatsber. 

 der Berl. Akad. d. Wiss. 1852 u. 1853). Pringsheim, Ueber die nacktfiissigen Vorkeime der Charen 

 in his Jahrb. f. wiss. Bot. Bd. III. 1864. Nageli, Die Rotationsstromung der Charen (Beitr. z. 

 wiss. Bot. Bd. III. 1860, p. 61). Thuret, Sur les antheridies des Cryptogames (Ann. d. sc. nat. 1851, T. 

 XVI. p. 19). Montagne, Multiplication des charagnes par division (Ann. d. sc. nat. 1852, T. XVIII. 

 p.65). Gb'ppert und Cohn in Bot. Zeit. 1 849. De Bary,Ueber die Befruchtung der Charen (Monatsber. 

 d. Berl. Akad. 1874, Mai) ; and Zur Keimungsgeschichte der Charen (Bot. Zeit. 1875). 



