THE SOMATIC ORGAyiZATION* OF THE P1I.EUPHTCE.E 123 



Ph:eophyceie have undoubtedly originatt?d directly from free-Hoating 

 autotrophic plankton," the factoi-s in the life of which have been set 

 forth in detail in a previous memoir (^The Btiihlinc/ of an Aiito- 

 irophic FlageUute). The next stage to be ix)stulated is the genesis 

 of marine benthon, when the rising sea-bottom of the primieval 

 ocean at last made it jx)ssible for sunken Hagelkites to attach them- 

 selves by their tlagella upon a rocky stratum within range of sutli- 

 cient illumination for the m:iintenance of continued existence, and so 

 acquiring an increased supply of gases and salts from the ever- 

 Mowing water. The anclioivd organisms became encysted and gnulu- 

 ally adapted themselves to the new benthic conditions. The proilucts 

 of cell-division, instead of separating like plankton units, began to 

 hold together and form associations. Dr. Church shows why the 

 uniseriate filament would have by far the best chance in the strui^gle 

 for existence, and adopts the tilamentous soma as indicating the main 

 line of progression. He then discusses the question of apical growth, 

 the origin of ramification, and the meaning of the branch, also the 

 strengthening of the filament to resist the tug of the moving water. 

 AVe have now reached the stage of Ectocarpoid Benthon, and then 

 pass through several chapters which treat of adaptations evolved to 

 meet the violence of wave-action, as the rocky bottom was elevated 

 towards the sm-face — the Cable type of axis {Cho/'Jaria), the Multi- 

 septate Cable (Chorda Fihim), Corticated types, Parenchymatous 

 types {Laminan'a and Fiicus). This leads on to a consideration of 

 the evolution of growing points and of systems of ramification, the 

 meaning of symmetry, phyllotaxis, differentiation of space-form, 

 bilateral symmetry, and the theory of members. The evolution of 

 the leaf -member of higher plants is neatly displayed in twelve 

 successive phyletic stages, in the first five of which the Pliieo- 

 phyceie figure. Haptera or Crampons (forcshadowing the roof of 

 higher plants), Pneumatocysts, Gametophores, and the elaboration of 

 differentiated shoot-systems, next come under consideration, and arc 

 followed by tissue-dift'erentiation, mucilage-liaii-s, and ducts. After a 

 few brief chapters on the Pulvinate thallus, the Disc-t,vpe, the Pal- 

 melloid type, and on epiphytes, parasites, and endophytes, we come 

 to the final chapter. This affords a stimulating account of the 

 author's broad views on the alga? in general, and of their structurc 

 in relation to that of the higher plants of the dry land, and on the 

 geological history of the alga? paralleled by that of zoological 

 organisms. Dr. Church possesses a remarkable gift for appreciatino: 

 and realising the conditions in which the evolution of the marine 

 flora took place ; and this has enabled him to construct a closely 

 reasoned account of how the algie adapted themselves to the graduallv 

 changing conditions of their oceanic environment. He sets forth 

 innumerable facts and cogent deductions which prepiire the wav for 

 his brilliant conception of a Land Flora derived from Oceanic 

 migrants equip^ied with all the potentialities of stem, leaf, and root, 

 as described in a previous memoir, Thalassio^fJii/ta and the Stihuerial 

 Transmigration. 



A. G. 



