22 Alg<c 



groups which could no longer be tolerated in the sense in which 

 they were originally proposed. 



Chodat, from observations on the lower green Alga?, both in 

 a state of nature and in cultures, traces the principal groups 

 of the Chlorophycese back to the Palmellaceas, one of the lowly 

 families of the order Protococcoidese. He recognizes three 

 important tendencies which rule the lower green Algse: (1) the 

 zoospore-condition, the other two conditions being only transient ; 

 (2) the sporangium-condition or unicellular motionless stage, the 

 other conditions being realized accidentally; (3) the Tetraspora- 

 stage, where non-motile cells are connected by regular cell-walls 

 at right angles. 



Blackman follows somewhat on these lines, but he considers, 

 along with others, that all the tendencies of the lower Algce have 

 had an origin in the motile unicellular Chlamydomonads. Among 

 the families of lower Algae constituting the group of the Proto- 

 coccoidese, he observes three divergent vegetative tendencies : 

 (1) a Volvocine tendency towards the aggregation of motile 

 vegetative cells into gradually larger and more specialized motile 

 true co3nobia ; (2) a Tetrasporine tendency towards the formation 

 of aggregations by the juxtaposition of the products of septate 

 vegetative cell-division to form non-motile organisms of increasing 

 definiteness and solidarity; (3) an Endosphaerine tendency towards 

 the reduction of the vegetative division and septate cell-formation 

 to a minimum. The simplest forms which exhibit any one of these 

 three tendencies seem clearly to diverge from species of the genus 

 Chlamydomonas, and these motile organisms must be regarded 

 as the real primitive form of green plant and the foundation 

 stone, so to speak, of the vegetable kingdom. Of late much work 

 has been done at the genus Cltlami/domonas by Goroschankin, 

 Franct^, Dill, Klebs, and Wille, and now the genus is brought 

 into still more prominence. It has been found to contain some 

 twenty-nine species which are remarkable for the constancy 

 of their cytological characters. Unfavourable conditions produce 

 in this genus the ' Palniella-cofidition.' This is the beginning of 

 a vegetative non-motile existence such as predominates in the 

 Palmellacese. In the latter family the cells at intervals in their 

 life-history escape from their walls, develop cilia, and return to the 

 motile state as zoogonidia. Blackman remarks that the "formation 

 of zoospores is then nothing but reversion to an ancestral type of 



