54 Chlorophycece 



Multiplication by cell-division occurs in many of the lower 

 forms of the Protococcoideae and in the Desmidiaceae. In the 

 Zygnemaceae, and particularly in the smaller species of Spirogyra, 

 the filaments often dissociate into solitary cells each of which then 

 divides and forms a new filament. 



Asexual reproduction by zoogonidia is general throughout the 

 class, although there is a notable exception in the Conjugate, in 

 which motile reproductive cells are entirely wanting. In many of 

 the Chaetophorales, Microsporales and Protococcoideae reproduction 

 takes place by non-motile spores which may be either akinetes or 

 aplanospores. Asexual spores are also more rarely found in the 

 Conjugate, having been observed in Zygnema, Spirogyra, and in a 

 few Desmids, and they are formed normally in the rare genus 

 Gonatonema. 



Sexual reproduction occurs in most of the families of green 

 Algae, and may be either isogamous or heterogamous. In iso- 

 gamous reproduction the sexual organs are gametangia, usually 

 giving rise to planogametes which conjugate and produce a zygo- 

 spore. In the Conjugatae only aplanogametes are found. Many 

 planogametes are generally produced from one gametangium, but 

 only one aplanogamete. In heterogamous reproduction the sexual 

 organs are oogonia and antheridia, and the gametes consist of 

 oospheres and antherozoids. In all cases with the exception of 

 Herposteiron, the oosphere remains in situ in the parent plant, 

 being fertilized within the oogonium, and the result of fertilization 

 is an oospore. The oogonia are always unicellular, and, except in 

 Cylindrocapsa and some species of (Edogonium, so are the anthe- 

 ridia. Only one oosphere is produced in an oogonium, except in 

 Sphceroplea, and one, two, or many antherozoids may arise from an 

 antheridium. 



The gametophyte is the principal generation, the sporophyte 

 being generally represented by the sexually-produced spore. In 

 Coleochcete, in (Edogonium, and in Mougeotia very rudimentary 

 sporophyte generations consisting of several cells do exist. 



Of all freshwater Algae the Chlorophyceae have the most varied 

 habitats. They are found in every possible damp or wet situation 

 and some are epiphytes, others endophytes, and a few are even 

 parasites 1 . 



1 Phyllosiphon Arisari Kiihn (in Sitzungsber. d. naturf. Ges. in Halle, 1878) is 

 a parasitic Alga observed only on the leaves of Arisarum vulgar e in Italy and the 



