52 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 

 a new 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. 



CHARACEAE. 



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

 very closely allied to any of ihem. 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 aniheridia [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-emhryo, 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. 



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

 der. Berl. Akad. d. Wiss. i8.S2 u. 1853). — Pringsheim, Ueber die nacktfiissigen Vorkeime der Charen 

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

 wiss. Bot. Bd. III. i860 p. 61). — Thuret, Surles antheridies des Cryptogames (Ann. d. sc. nat. 1851, T. 

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

 p. 65). — Goppert und Cohn in Bot. Zeit. 1 849. — De Bary.Ueberdie Befruchtungder Charen (Monatsber. 

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



