CLASSIFICATION OF THE PRIMORDIA 77 



conclude that the transverse axes of all the cells are probably 

 in one plane. ^ 



The conjugating processes have (apart from their position) 

 certain simple measxirable properties (length, diameter) which 

 belong to the fifth group (dimensions) in § 57. The existence 

 of the sexual outgrowths is a result of a differentiation within 

 the limits of one cell and ought therefore to be brought into a 

 sixth group of properties. (Compare the five groups in § 57.) 

 The properties of the outgrowths are awakening, arrested and 

 rather caducous or deciduous. Their sensitive period very 

 probably begins after that of all the other properties. 



§61.— THE UNIAXIAL SYSTEM IS A PRIMARY 

 SYSTEM. — Since the segments (cells) of a Spirogyra follow 

 each other according to one axis, I call an adult specimen of 

 this plant a uniaxial system. This is the simplest system of 

 segmentation ; it is observed again and again in the animal 

 and in the vegetable kingdom.^ It is a primary system from 

 which several other systems are derived. 



Since the properties of the living beings are ordered with 

 reference to their axes, the determination of the axes is of high 

 importance for the exact definition and the measurement of 

 each property. 



The study of the uniaxial system and its derivatives is con- 

 tinued in § 69. In §§ 62-68 I mention foiir special systems of 

 segmentation which have merely indirect relations (if any 

 relation at all) to the uniaxial system and about which I have 

 incomplete information. 



§ 62.— SPECIAL SYSTEMS OF SEGMENTATION. I. 

 RADIAL SYSTEM. — Under this name several different 

 systems are confounded. A radial system is observed in 

 Polyps. The radial system of the Echinoderms has a different 

 origin. 



The radial system of the spiral and pseudo-cyclic flowers pro- 

 ceeds indirectly from the uniaxial system, and is, on the other 

 hand, in relation with the sectorial symmetry which prevails in 

 the true cycUc flowers. 



See also Pediastrum tetras, § 64, Fig. 3. 



^The egg e has probably, within its mother-cell, a definite position with 

 regard to the transverse axis 6 of the latter. On the other hand, the position 

 of the transverse axes 6* of the cells of the specimen produced by e is probably 

 already determined in the egg e. It would be interesting to know the relative 

 position of b and 6'. 



* Examples : The hairs of innumerable plants (here the segments are uni- 

 cellular), the antenna of an insect (here the segments are so-called joints), etc. 

 In the simplest case a uniaxial system includes only two segments ; for instance, 

 the teleutospores of Puccinia, the first pair of cells produced by the segmenta- 

 tion of the egg in animals and plants, etc. 



