RECONSTITUTIONAL PATTERNS IN EXPERIMENT 423 



revolving wheel. That Loeb's results may have been due to an oxygen 

 gradient decreasing downward is perhaps possible. In general, gravity 

 or, as will appear below, even high-speed centrifuging does not seem to be 

 a very important factor in determining or altering axiate pattern in ani- 

 mals, though there are some cases in which one or the other factor is 

 effective; and further experiment, particularly with the very high centri- 

 fuge speeds now possible, may bring new evidence on this point. 



B 



Fig. 143, A-H. — Early development of Fiicus. A, normal development with plane of cell 

 division at right angle to axis indicated by rhizoid outgrowth, separating a rhizoid cell and a 

 thallus cell; 5-Z), altered relations of rhizoid outgrowth and division plane resulting from 

 change in direction of illumination; E-H, bipolar forms resulting from periodic change of 180° 

 with respect to direction of light. 



EXPERIMENTAL ALTERATIONS OF EMBRYONIC AND AGAMIC 

 PATTERN BY ENVIRONMENTAL FACTORS 



So far as data are available, pattern in most eggs and early embryonic 

 stages appears to be relatively stable in relation to external differentials, 

 but in some forms new pattern can be determined experimentally by such 

 factors. Perhaps the most interesting case is the egg of the alga Fucus. 

 This egg apparently possesses a polarity when shed, since it can develop 

 the axiate rhizoid and thallus in complete darkness without any evident 

 relation to external factors. The first indication of development in the 

 originally spherical cell is a bulging or outgrowth from a part of its sur- 

 face, followed by a cell division in a plane transverse to the axis of the 

 outgrowth (Fig. 143, A). The outgrowth represents an early stage of the 

 first rhizoid and, with various methods, shows a gradient with high end 



