38 



behaves in the same way. The outer layer of its normal 

 thallus is composed ox "palisade tubes", swollen to a club 

 shape, and arranged perpendicular to the surface. On their 

 tips arise the slender unbranched "trichome tubes" which 

 are sharply cut off from them. All these differences are 

 lost during longer cultivation, The trichome tubes be- 

 come similar to the others, if still at all recognizable, 

 as such, they branch e^ctensively, etc. It is not known 

 as yet whether in these and similar cases the arrested de- 

 velopments may be traced back to scarcity of light, insuf- 

 ficient oxygen supply, or to other factors. Finally the 

 phenomena of arrestment exhibited by Struvea should be con- 

 sidered. They furnish indeed nothing essentially new, but 

 may find mention here because of their biological interest. 

 According to ¥/eber van Bosse -^ . Struvea delicatula lives 

 at times in symbiosis with a fungus (Halichondria) but 

 then only develops filaments, resembling Vaucheria, instead 

 of the characteristic extensively branched shoots, just 

 as do the Udotea and Codium specimens in our cultures. The 

 author compares the form of the alga, simplified by sym- 

 biosis, to Spongocladia vaucheriaef ormis , Undoubtedls^ , 

 her observations may be placed in line v>rith those quoted 

 above. 



Also in the case of the more simply formed Siphon- 

 aceae, the distinct formation of different cell parts is 

 omitted under certain- conditions, for example in Bryopsis. 

 33 In Vaucheria the vegetative parte of the filaments are 



known to be all alike^ Only those parts of the cell serv- 

 ing for propagation are differently constructed. That even 

 this difference in form may be lost, is proved by the oog^ 

 onia which develop vegetatively. 



In the case of the Matomeae and Peridineae also , in 

 which highly organized cell- forms are abundant, analogous 

 "simplifications" must be found if one looks for them. 

 Hattray described abnormal forms for Aulacodiscuc , in which 

 the characteristic protuberances were lacking, 3 cf the un- 

 icellular Chlorophyceae , Scendesmus acutus. fo r exaraple, 

 comes under our consideration, which with an excess o." 

 organic food, may lose its tips,^ etc, 



CELL MSMBRAJSE 



Arrested development of the cell membrane is expressed 

 for the most part by the partial or entire cessation of its 

 secondary growth in thickness. The cells of the epidermis, 

 the ducts, the sclerenchyma and collenchyma cells then 

 show only moderately thickened ?/alls , or the formation of 



1, Etudes s, des, algues de 1' archipel malaisien I. Ann 

 Jard. Bot. Buitenzorg, 1890, Vol. VIII, p. 79. 



2, Klebs, Beding. d. Portpfl. bei einigen Algen und 

 Pilzen. Jena k896, p. 102. 



3, notes on some abnormal forms of Aulacodiscus Bhrb, 

 J. of Bot., 1888, Vol, 2XVI, p. 97. 



4, Beijerinck, Kulturversuche mit Zoochlorellen, 

 Lichenengonidien u. s, w. Botan. Zeitg. , 1890, Bd. XLVIII- 

 p. 724. 



