NOTES ON FRESHWATER ALGX 39 
pone no. 957, satin eae ta p. 26. Crass. cell. veget. 11°5- 
; diam. ~~ . 27-33 p, max. 384°5-48 »; crass. strat. 
ok geiak. 7-85 p. 
Hab. In ditches near the Lizard, Cornwall. Also Llyn 
Geirionedd, N. Wales 
ese examples were rather less than Wittrock’s original 
Swedish specimens, but otherwise were precisely similar. We 
have previously recorded ‘this alga from Scotland (Journ. Bot. 
1898, p. 98). 
22, M. eLecantuta Wittr. in Bih. till K. Sven. Vet.-Akad. 
Handl. Bd. 1, me 1, 1872, p. pe hss f. 5-8. 
Hab. Llyn-y-cwm-ffynon, N. Wales 
23. De ‘adhe a ae sp. n. “PL 446, figs. 1-9.) Fila 
longa, flexuosa, facile dissociata, ad oe sis multe constricta ; 
cellulis vegetativis cylindricis, diametro 2}-6}-pl wr. ote api- 
cibus rotundo-truncatis, pyrenoidibus 2 in chiotoplastida ida singula ; 
zygosporis rotundo-quadratis, lateribus rectis vel feviaitilis deknsts. 
Saar an post dissociationem filorum in cellulis singulis. ng. 
cell. 25-50 yw; lat. cell. 7°7-8°6 »; diam. zygosp. 21-25 p. 
S ‘a small stream an the izard, Cornwall. 
This remarkable plant is the most fragile of any of the described 
alge belonging to the subfamily Zygnemee. The filaments rhe 
up into individual cells most readily, and conjugation only occ 
between : get of isolated cells. The solitary chloroplastid, “which 
usually extends from one pole of the cell to the other, and c 
two nbida: is sometimes restricted to the equatorial Seorcs of 
the cell, fe at the same time retains a more or less compressed 
character. When in filaments hits i is a most evident constriction 
between the cells, and the whole filament is sheathed in a somewhat 
conspicuous gelatinous envelope.. Conjugation is exactl 
lants 
certain of the Desmidiacee. In fact, this plant seems to be one of 
the algex Pras 7 which the gradual Peet of the " Desmidiaicas has 
taken place. It has been well proved that the Desmids are a 
degenerate family of the Conjugate, and no form of the Zygnemacee 
n met with which illustrates this degeneracy better than 
Debarya desmidioides. It is one of those alge which add a still 
stronger link to the chain of evidence ehich goes to prove that the 
fa. — Desmidiacee is @ $y PEE group of the Conjugate, and that 
the group has arisen by a loss of the filamentous condition and a 
degeneration of sexual pase accompanied by an increase of 
orphologi 
scheme of evolution of the genera of Desmids that has already 
been advocated (cfr. G. S. West, ‘On Variation in the Desmidiea 
i i inn. 
"eThe formation of the aygospore in D. desmidioides takes aa 
