636 PATTERNS AND PROBLEMS OF DEVELOPMENT 



isolation as a factor in the origin of buds. In the repetitive budding of 

 pelagic tunicates the orderly periodicity is difficult to account for, except 

 in terms of dominance and physiological isolations. 



Apparently the longitudinal axis of the tunicate bud which originates 

 as a local activation represents transformation of a more or less radial 

 pattern into a longitudinal pattern by differential growth, as in other 

 buds; but dorsiventrality and asymmetry in these buds are definitely 

 oriented in relation to the parent pattern or to a local factor in the stolon 

 or other budding region. The winter buds of some forms are more like 

 fissions than buds."* They, or some of them, apparently reconstitute from 

 the part of the parent pattern persisting in them, but the reconstitution 

 of experimentally isolated pieces of ascidian bodies and stolons indicates 

 that new polarities may arise in such pieces in relation to section and 

 perhaps to other factors (p. 369). But whether the specific asymmetry 

 pattern of the ascidian can originate in relation to a new polarity and 

 independently of parental pattern seems not to be known. 



The sponge gemmule is sometimes regarded as a sort of internal bud 

 but probably resembles more closely an aggregation of dissociated cells 

 than a bud, except that it does not contain all the differentiated tissue cells 

 that may be present in an aggregate. Like the aggregate, the cell mass 

 of the gemmule apparently does not possess a definite organismic pattern 

 until subjected to an environmental differential, usually that between 

 free surface and surface in contact, presumably an oxygen differential. 

 The canals center, and oscula develop on the free surface. 



MULTICELLULAR AXIATE PLANT PATTERN FROM CELL AGGREGATES 



In certain plants multicellular axiate patterns, often multiaxiate pat- 

 terns, develop from aggregates of myxamoebae, of diatoms, or of hyphae 

 of fungi. These patterns are orderly and definite in character, and some 

 of them attain considerable morphological differentiation. The features 

 and problems they present are, or should be, of much interest to the de- 

 velopmental physiologist. 



DEVELOPMENT OF PATTERN IN ACRASIEAE 



In this small group of plants, often regarded as more or less closely re- 

 lated to the myxomycetes, axiate pattern originates in definitely directed 

 motor reactions of separate amoeboid cells. Two forms, Polyspondylium 



'^See, e.g., Berrill, 1935. 



