286 



Ulotrichales 



U. zonata, and they do not apply to several of the smaller species of Ulothrix *. Four of 

 Klebs' main conclusions were : (1) that if, after cessation of zoospore- formation, the 

 filaments were transferred from nutritive solutions to water, then zoospore-formation 

 recommences ; (2) that zoospores were formed by transferring filaments from a nutritive 

 solution to water and then putting the cultures in the dark for three days ; (3) that 

 transference of the filaments from running water to quiet water, or bringing from a 

 natural habitat into a room, resulted in zoospore-formation, the cause being attributed 

 to the diminution of the amount of air in the water ; (4) that observations were 

 against a rise in temperature being a special cause in inducing the formation of 

 zoospores. 



Klebs' first statement does not apply to the smaller species of Ulothrix and repeated 

 experiment has failed to confirm it in U. zonata. Experiments extending over two years 



Fig. 183. A, part of filament of Ulothrix sequalis Kiitz. to show single chloroplast with pyrenoid 

 (py). B and C, U. zonata (Web. & Mohr) Kiitz. B, part of filament showing germination 

 of microgonidia (which have never been motile) to form new plants ; C, similar germination 

 of macrogonidia. D, Stichococcus varlabilis W. & Gr. S. West. E, aquatic form of 

 S. flaccidus (Kiitz.) Gay, only in outline except for one cell which shows partial frag- 

 mentation of chloroplast. F, S. bacillaris Nag. All x 500. 



do not bear out his second statement in the case of either U. tenuissima or U. subtilis. 

 Concerning his third statement this was not found to be true in the case of U. zonata 

 and U. subtilis unless the transference was accompanied by a decided change in tem- 

 perature. In contrast to his fourth statement experiments conducted over a long period 

 with U. zonata, U. sequalis, U. tenuissima and U. subtilis lead to the conclusion that a 

 rapid alteration in temperature (whether increase or decrease) is a direct incentive to 

 zoospore-formation, and is really a factor of great importance in the production of the 

 zoogonidia of Ulothrix. 



1 Various species of Ulothrix have been under experimental investigation by the author and 

 Miss C. B. Starkey in the botanical laboratory of the University of Birmingham for upwards of 

 two years. 



