CONJUGATION IN UNICELLULAR FORMS 163 



the male germ-nucleus of phanerogams is " cyanophilous," the female 

 " erythrophilous," as described by Auerbach in animals. Stras- 

 burger, while confirming this observation in some cases, finds the 

 reaction t9 be inconstant, though the germ-nuclei usually show 

 marked differences in their staining-capacity. These are ascribed by 

 Strasburger ('92, '94) to differences in the conditions of nutrition ; by 

 Zacharias and Schwarz to corresponding differences in chemical 

 composition, the male nucleus being in general richer in nuclein, and 

 the female nucleus poorer. This distinction disappears during ferti- 

 lization, and Strasburger has observed, in the case of gymnosperms 

 (after treatment with a mixture of fuchsin-iodine-green) that the 

 paternal nucleus, which is at first "cyanophilous," becomes "erythro- 

 philous," like the egg-nucleus before the pollen-tube has reached the 

 egg. Within the egg both stain exactly alike. These facts indicate, 

 as Strasburger insists, that the differences between the germ-nuclei 

 of plants are as in animals of a temporary and non-essential character. 



E. CONJUGATION IN UNICELLULAR FORMS 



The conjugation of unicellular organisms possesses a peculiar inter- 

 est, since it is undoubtedly a prototype of the union of germ-cells 

 in the multicellular forms. Biitschli and Minot long ago maintained 

 that cell-divisions tend to run in cycles, each of which begins and 

 ends with an act of conjugation. In the higher forms the cells pro- 

 duced in each cycle cohere to form the multicellular body ; in the 

 unicellular forms the cells separate as distinct individuals, but those 

 belonging to one cycle are collectively comparable with the multi- 

 cellular body. The validity of this comparison, in a morphological 

 sense, is generally admitted. 1 No process of conjugation, it is true, is 

 known to occur in many unicellular and in some multicellular forms, 

 and the cyclical character of cell-division still remains sub judice* 

 It is none the less certain that a key to the fertilization of higher 

 forms must be sought in the conjugation of unicellular organisms. 



The difficulties of observation are, however, so great that we are 

 as yet acquainted with only the outlines of the process, and have still 

 no very clear idea of its finer details or its physiological meaning. 

 The phenomena have been most closely followed in the Infusoria by 

 Biitschli, Maupas, and Richard Hertwig, though many valuable ob- 

 servations on the conjugation of unicellular plants have been made 

 by De Bary, Schmitz, Klebahn, and Overton. All these observers 

 have reached the same general result as that attained through study 

 of the fertilization of the egg ; namely, that an essential phenomenon 



1 Cf. p. 41. 2 Cf. p. 129. 



