PHYLOGENY 



chemically quite similar to chlorophyll, and it has been shown by van Niel 

 to have photosynthetic activity. Hence there is a reasonable probability 

 that the blue-green algae, the most primitive of the green plants, have 

 been derived from the sulfur bacteria. Some other possibilities have also 

 been suggested. The spirochaetes have a type of motility which suggests 

 that of some of the Protozoa, but they do not have a well-defined nucleus. 

 They have been variously classified with the bacteria and with the Proto- 

 zoa. Although their general biology appears to tie them in more closely 

 with the bacteria, it is possible that they are in fact a transitional group. 

 Finally, the slime bacteria show some similarities to the slime molds, and 

 it has been suggested that this is based upon phylogenetic relationship. 

 However, the cells of slime bacteria live in a secreted nonliving slime, 

 while slime molds are multinucleate masses of protoplasm. Any or none 

 of these hypotheses may be correct. There is no direct evidence available, 

 and perhaps there never will be, for these events must have preceded by 

 long ages the formation of the oldest rocks which bear fossils of any value 

 for study. Further, the lowest plants, the algae and fungi, include many 

 groups of quite diverse nature, their primitiveness being their principal 

 common character. While some of these may have had a common origin 

 from the bacteria, it is possible that each of these phyla of primitive plants 

 may have arisen independently from a different bacterial ancestor. 



SUBKINGDOM THALLOPHYTA 



The plant phyla which formerly were grouped together as a single phylum 

 Thallophyta are those which are most closely related to the bacteria. The 

 Thallophyta are now treated as a subkingdom, including all plants which 

 reproduce without the formation of an embryo within the ovary of the 

 maternal plant. This subkingdom includes ten phyla ranging in complex- 

 ity from the bacteria to algae nearly as complex as the simpler vascular 

 plants. Of these, three phyla, the Schizomycophyta or bacteria; the Myxo- 

 mycophyta or slime molds; and the Eumycophyta or true molds and yeasts 

 comprise the old group Fungi. The relationships of these groups are not 

 at all clear, but the latter two appear to be terminal groups, that is, they 

 have not given rise to others. As was already indicated, the slime molds 

 may have been derived from the slim(> bacteria. But the slime molds move 

 by ameboid movement. They reproduce by means of flagellate, ameboid 

 swarm cells. As these swarm spores fuse in pairs, a type of sexual repro- 

 duction is represented. Many mycologists feel that the Myxomycoplnta 

 are more closely similar to the Protozoa than to any other group, and they 

 have even been classified as Protozoa under the namc^ M\cc»t()zoa. Those 

 who support this viewpoint regard them as at least transitional between 

 the two kingdoms. The Eumycophyta are similarly obscure as to their 

 origin. In structure and function, they show many parallels to the green 

 algae, and so they have been thought to be derived from this group. But 

 their zo()sp()r(\s res(Miible those of the slime molds and show ameboid 

 movement. Hence it is possible that the Nh'xomNcophvta ha\'e given rise 

 to the Eumycophyta. These ilagcUatcd zoospores closely resemble some 



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