GROUP I. THALLOPHYTA: ALG^E : CHLOROPHYCEJ}. 243 



rounded by a delicate membrane within which they come to rest and cohere 

 to form a Pediastrum=-plant. 



In Coalastrum and Sorastrum the gonidia formed in the mother-cell either afc 

 once unite to form a new coenobium, or they may be set free, and then each 

 undergoes repeated division to form a new coenobiunij In view of the 4 state- 

 ment that these two genera are not coenocytic, but cellular, and of the fact that 

 in them the coenobium may be formed by cell-division, it appears that their 

 affinities are rather With the Protococcoideae than with the Siphonoideae.- 



Series IV. OONFERVOIDE.E. The forms included in this series maybe arranged 



in tha following orders : 

 Sub-series A. Azoosporeae : no zoogonidia or zoospores* 



Order 1. Conjugate : sexual reproduction by aplanogametes* 

 Sub-series B. Zoosporea? ; asexual reproduction by zoogouidia and zoospores. 

 IsogamoMs fders : 



Order 2. Ulothricaceae : body filamentous, unbranched. 



Order 3. Chaetophoraceae : body filamentous, branched. 



Order 4. Ulvaceae : body a flat or tubular cellular expansion. 

 Oogamous Orders : - 



Order 5. CEldogoniaceae: body filamentous, unbranched (except Bulbochaete) . 



Order 6. Coleochaatacea : body filamentous, branched ; oogonium with a 

 trichogyne ; sporophyte multicellular. 



An asexual formation of spores takes place in all the Confervoideas, except the 

 Conjugates. The sporophyte^ in all cases in which it is fully knoWiij gives rise 

 to zoospores., The gametophyte multiplies itself by means of zoogonidia, and 

 in some cases (Chaetophoraceae) by means of resting gonidia s The gonidangia 

 are not differentiated, as any cell of the body may act as one. Several zoospores 

 are usually developed in a single sporangial cell, but in some casts only one 

 (e.g. zoogonidia of CEldogonium and Coleochaste, zoospores of ColeOchsete). 



A sexual formation of spores takes place in all the Confervoideas ; in the 

 isogamous forms the product of conjugation is a zygospore ; in the oogamous 

 forms it is an oospore. In the isogamous forms the sexual organs, or game- 

 tangia, are not differentiated; any or all of the cells of the body may act as 

 gametangia ; the sexual cells are (except in the Con jugatae) free-swimming simi- 

 lar planogametes ; in the Conjugates the gametes are not set free into the water, 

 and they are not ciliated. In some cases (e.g. Ulothrix, Chroolepus) the piano- 

 gametes, if they fail to conjugate, are capable of independent germination, thus 

 showing their imperfect sexual differentiation. The plauogametes usually 

 differ from the zoogonidia in being smaller. In the oogamous forms the sexual 

 organs are antheridia arid oogonia ; they are more or less markedly differen- 

 tiated. The sexual cells are oospheres and spermatozoids* The oospheres are 

 formed singly in the oogonium. The spermatozoids are formed singly in the 

 mother-cell; they resemble the zoogonidia of the respective plants, but are 

 smaller and are not green. 



The life-history of the Confervoideae has been investigated with success in 

 only a few forms (some Conjugate, Ulothrix, CEdogonium, Coleochaete). In 

 the Conjugatae, as there is no asexual produtcion of spores, there is no alterna- 

 tion of generations ; in the others such an alternation can be traced. In these 



