ALGA E — PHAEOSPOREA E. 



67 



The growing-point is at the base of the filament, which consists of a single cell-row, the 

 cells of which continually divide and multiply ; the uppermost divide by longitudinal 

 walls and pass into the permanent state; in older filaments all the cells do so ultimately, 

 and are then no longer capable of growth, but form a permanent cellular tissue. The 

 forms known as Mesogloeaeare only filaments of £"1;/'^- 

 Cdf'pKS of somewhat more complex construction ; their 

 branches are intertwined and often fused with one 

 another by the conversion of their cell-walls into a 

 mucilage, or, as in Desniarestia^ StilopJiora^ &c., grow 

 together into a tissue. 



We have the authority of Goebel for a conjugation 

 of similar gametes produced in plurilocular sporangia 

 in the case of Ectocarpus pusillus and Giraudia splia- 

 celarioidesj Berthold^ describes the same conjugation 

 in Ectocarpus siliculosits and Scytosiphon, but with a 

 difference. The conjugation in the two first cases is 

 the same as in Ulothrix^ &.c., and only gametes from 

 different sporangia unite together. The following is 

 Berthold's description of the process in E. Siliculosus 

 and Scytosiphon. Someof the swarm-spores produced 

 in the plurilocular sporangia are male gametes, others 

 are female, and both are of the same shape and 

 size. While the male cells are still moving actively 

 about, the female early attach themselves by one of 

 their cilia to some fixed body to which they draw 

 closer up by shortening and finally drawing in the 

 cilium entirely, the second cilium also being drawn in. 

 In this way the female swarm-spore becomes the 

 oosphere, with which a male swarm-spore may now 

 coalesce. There is no receptive spot. Both kinds of 

 gametes may germinate without conjugation, but the 

 plants produced from the male swarm-spores are some 

 of them very weakly. The zygospore or oospore also 

 produces a young plant of Ectocarpus directly in ger- 

 mination. 



b. The Sphacelarieae ', in which no sexual pro- 

 cess has hitherto been found, are chiefly distinguished 

 from the Ectocarpeae by their mode of growth. The 

 growing-point of the main and lateral axis is here ter- 

 minal, and the summit is occupied by a large apical 

 cell, which forms segments by transverse walls ; fur- 

 ther differentiation of tissue then takes place in the 

 segments thus formed (P'ig. 42), each segment-disc 

 being divided by longitudinal walls. There are many interesting details in the structure 

 of the thallus which we cannot enter into here. But it should be noticed (see Fig. 42) 

 that in Stypocaulojt, as Geyler has shown, the apical cell is as a rule the only growing 

 part of the thallus ; the lateral axes are formed on it, while these proceed in other 



Fig. 42. Summit of a branch of the thallus 

 of Slyfocaulon scoparium. s apical cell (here 

 the only growing part of the thallus) which is 

 forming the rudiment of a branch at r ; y, x 

 older branches ; k hairs. The apical cell is 

 divided above its base by the walls I* and Il>, 

 and each segment is again divided by a trans- 

 verse wall II», lib, into t^vo disc-shaped cells 

 in which compartments are formed by longi- 

 tudinal walls. After Geyler. 



^ That this observer saw no conjugation in the case of Ectocarpus pusillus does not prove th.it 

 none takes place ; we must wait for fresh investigations. 



2 Pringsheim, Ueber den Gang der morpholog. Differenzirung in der Sphacelarienreihe (Abh. 

 d. Berl. Akad. 1873).— Geyler, Zur Kenntniss der Sphacelariecn (^Pringsheim's Jahrb. f. wiss. Bot. 

 IV. Bd.). — On the gemmae see Janczewski, Les propagules du Sph. cirrhosa (Mem. do la soc. nat. 

 de Cherbourg, T. XVIII. 1872J. 



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