1 86 ALG^ 



Any classification of Algae which attempts to follow the lines of 

 afiinit}; — in other words, any natural system of classification — must be 

 based on a consideration of both the vegetative and the reproductive 

 organs. All the families of Algae appear undoubtedly to have sprung 

 from the ProtococcoidE/E, and their further development has taken 

 place in three directions — the perfection and differentiation of the in- 

 dividual cell, the association of cells into coenobes, and cell-division. 

 The production of coenobes may be supposed to start from such forms 

 as Botryococcus among Protococcacea ; the first step in the develop- 

 ment of the CcENOBi^ being the Sorastrem, including Sorastrum, 

 Coelastrum, and Selenastrum, motile colonies of non-ciliated cells, with 

 no known production of zoospores. The series attains a much higher 

 development in the Pandorinem, including Pandorina, Gonium, and 

 Stephanosphsera, where reproduction is effected by the conjugation of 

 zoogametes. Simple organisms like Chlamydomonas and Chlamydo- 

 coccus, consisting merely of conjugating zoogametes, are possibly retro- 

 gressions from the higher forms, though they may also be stages in a 

 direct ascent from Protococcus. Eudorina, with a rudimentary differ- 

 entiation of antherozoids and oospheres, unquestionably indicates the 

 line of development of Volvox, in which this differentiation is more 

 strongly developed. In Volvox we have the culmination of the attempt 

 of nature to evolve higher organisms out of coenobes. Hydrodictyon is 

 probably an aberrant member of this group, and the Pediastrem are more 

 or less nearly related to them. 



From the Eremobice the fuller development of the individual cell has 

 advanced a further stage in the Multinucleate, composed of the 

 Siphonodadacea and SipJwnea, and characterised by each individual 

 consisting of an enormously developed cell, often ramifying greatly and 

 attaining gigantic dimensions, and possessing several, often a very con- 

 siderable number, of nuclei. In the Siphonocladaceas the only known 

 mode of reproduction is by the conjugation of zoogametes ; and 

 Botrydium displays a distinct affinity with Botrydina among the 

 Eremobise. The Siphoneae or Coeloblastae, represented by Vaucheria, 

 are a higher development of the same series, in which true sexual organs, 

 oogones and antherids, are formed in addition to non-sexual zoospores ; 

 and in this genus culminates the striving after a higher development in 

 the elaboration of a single cell. 



A rudimentary cell-division is exhibited in the Nostochinea among 

 Protophytes, but accompanied by other conditions which prevented its 

 full success there. Where cell-division originated in the Protococcoideae 

 is not clear, probably in the Eremobiae ; we find it already fully developed 

 in the Confervoidee isogame, the members of which consist of a 



