328 Proceedings of the OJiio State Academy of Science 



out definite proof that the primitive plants were without sex. 

 With such an assumption the development of sex in all of its 

 phases becomes an evolutionary process, — a process becoming 

 more and more complicated as we go up the scale of organic be- 

 ings. If the archaic organisms were nonsexual, it is probable 

 that most of our lowest nonsexual forms have come through all 

 the geological ages in this primitive condition. They were prob- 

 ably specialized before their cells had developed a conjugation 

 process. It is evident that if plants came from nonsexual progen- 

 itors there should be no insurmountable difficulty in the way of 

 their return to the same condition after developing sexuality. 

 Vegetative propagation and parthenogenesis are present all along 

 the scale of organic ascent and are not impossible in any group 

 of plants. 



In the lower plants zoospore production is very general out- 

 side of the fission plants, and it is probable that sexuality had its 

 origin in practically all groups at the naked, motile stage of the 

 life cycle. Whenever conjugation takes place between walled 

 cells we may reasonably look upon the process as derived from a 

 naked cell conjugation. Such forms as Spirogyra and Mucor 

 become, from this point of view, extremely specialized types 

 rather than primitive ones. 



Now whatever may have been the ultimate cause of the evo- 

 lution of a conjugation process, it is commonly believed that the 

 immediate cause was a need of nutrition or rejuvenescence. If 

 an interchange of food could be brought about when a weaker 

 zoospore met a stronger one, the habit might become established, 

 and if two protoplasmic masses could learn to fuse more or less 

 completely on the approach of adverse conditions the fused in- 

 dividuals might have the advantage in passing through the un- 

 favorable period. For after conjugation the number of indi- 

 viduals would be but half of the previous number and the proto- 

 plasm would be more dense. In the lower forms conjugation 

 frequently takes place before the appearance of adverse condi- 

 tions and the zygote passes into a resting stage in which it can 

 endure both dryness and cold or a lack of food. There is also 

 a considerable reduction of the surface in proportion to the vol- 



