88 ] The Classification of Lower Organisms 



been demonstrated by Kylin ( 1933, 1934, 1937) in a wide variety ot genera, as Asco- 

 cyclus, Desmotrichum, Mesogloia, Eudesme, Leathesia, and Stilophora. In the more 

 primitive examples, the gametes are not visibly differentiated; in more advanced 

 ones, as Carpomitra and Desmarestia, different haploid bodies produce respectively 

 smaller sperms and larger eggs, the latter non-motile. 



There is a series of families, Ralfsiacea, Myrionematacea, Myriogloiacea, Meso- 

 gloiacea, and others, in which the diploid body consists of filaments differentiated 

 into different types. In the simplest of these, the germinating zygote produces in the 

 first place a minute thallus-like plate, generally epiphytic on other algae, one cell 

 thick, and consisting obviously of branched filaments of limited growth. From this 

 plate grow erect filaments. Some of these are simply cylindrical and appear nutritive 

 in function; others are attenuate, and may function in protection or in absorbing 

 materials from the water; yet others bear the reproductive structures, unilocular or 

 plurilocular or both. 



In the more advanced families, the diploid body, after passing through a Ralfsia- 

 or Myrionema-Vike stage, may produce a compacted column of filaments with a 

 terminal plate of apical cells. Besides adding cells to the column, the apical plate 

 gives rise to a fascicle of attenuate hairs projecting forward. Members of the families 

 Chordariacea, Sporochnea, and Desmarestiacea produce cylindrical or flattened 

 thallose bodies of tridimensionally placed cells differentiated into an outer layer of 

 small actively photosynthetic cells and an inner mass of nearly colorless cells. Super- 

 ficial hairs, growing in intercalary fashion, may become few, and growth may become 

 restricted to a single apical cell. 



By differences in the detailed manner of growth, Setchell and Gardner distin- 

 guished two orders among the thalloid forms just mentioned. It is evident, however, 

 that the thallose structure (and, likewise, differentiation of gametes) has developed 

 repeatedly and independently in the present group. Knowledge which would make it 

 possible to divide it into several recognizably natural orders is not yet available. 



Order 5. Cutlerialea [Cutlcriales] Bessey in Univ. Nebraska Studies 7: 289 ( 1907). 



Brown algae producing motile spores, the haploid and diploid bodies being macro- 

 scopically visible thalli, alike or different. 



This is a small group, of one family, Cutleriacea, with two genera, Zanardinia 

 and Cutlcria, known chiefly from the Mediterranean. In Zanardinia, both haploid 

 and diploid bodies are erect and rather freely branched. In Cutlcria, the haploid 

 bodies are of this description, while the diploid bodies are appressed and fan-shaped. 

 The distinct diploid bodies of Cutlcria were originally named as a different genus, 

 Aglaozonia. Falkenberg (1879) first showed that Cutlcria and Aglaozonia arc stages 

 of the same thing; Yamanouchi showed that they are respectively a haploid stage 

 with 24 chromosomes and a diploid stage with 48. 



The growing margins of the thalli consist of laterally compacted filaments grow- 

 ing by the divisions of a band of mcristematic cells which produce free hairs in the 

 distal direction and a continuous body of cells in the proximal direction. The latter 

 cells are capable of further division, and produce a body several cells thick, with 

 small cells rich in plastids on the surface and larger ones with fewer plastids in the 

 interior. 



Haploid individuals bear clusters of stalked plurilocular structures of two types, 

 almost always on different individuals, the larger ones consisting of fewer cells which 

 release eggs, the smaller of more numerous cells which release sperms. Both kinds of 



