j 20 THE E VOL UTION OF SEX. 



in the light of the theory we hold. Hence we prefer to follow some 

 accessible account, taken essentially from the morphological point of 

 view. We shall follow Prof. Vines in his article ' ' Reproduction — 

 Vegetable, ' ' in the Encyclopedia Britannica, at each stage, however, 

 endeavoring to interpret the facts, physiologically, in the light of 

 protoplasmic processes. 



i. The simple alga Protococcus — which, in the widest sense of that term, 

 every one knows in some form or other, on tree-stems, in pools, wells, and the 

 like — reproduces itself in a simple fashion. The cell divides into a number of 

 equal units or spores ; these are set free, are mobile for a while, eventually come 

 to rest, and develop to the normal size. A hint, however, of the beginning of a 

 difference is seen when the cell occasionally divides into a larger number of 

 smaller spores. These, however, show no difference in history. They settle 

 down, and develop just like their more richly-dowered neighbors. We find here 

 the occurrence of units of smaller size, that is to say, less predominantly ana- 

 bolic, but still these are able to develop independently. 



2. In a higher alga, Ulothrix — one of the series known as Confenxe — 

 both large and small reproductive cells are developed. The large ones 

 develop always of themselves, and so may the smaller forms. But the smaller 

 forms may also unite in pairs, and then start a new plant from the double capital 

 thus attained. When one of the smaller cells develops by itself, the result, in 

 some cases at least, is a weakly plant. They have what Prof. Vines calls an 

 "imperfect sexuality," for while they are in part dependent upon union with 

 other cells, they are not wholly so. They are anabolic enough, we may say, 

 sometimes to develop independently, but often they are individually too 

 katabolic for anything but weak independent development. In uniting, 

 however, in mutual nutrition, they are strong. The student will already see the 

 relative femaleness of the large units, the maleness of their smaller neighbors. 



3. A third stage is reached in another alga {Ectocarpus) which is peculiarly 

 instructive. This may separate off large cells which develop by themselves like 

 parthenogenetic ova. From other parts of the plant smaller units are liberated, 

 which generally, though not yet invariably, unite with one another before 

 developing. But between these smaller units a most important physiological 

 difference has been observed by Berthold. Some soon come to rest and settle 

 down, and with these their more energetic neighbors by-and-by unite. We 

 have here a very distinct beginning of the distinction between male and 

 female elements. The comparatively sluggish, more nutritive, preponderat- 

 ing^ anabolic cells, which soon settle down — are female ; the more mobile, 

 finally more exhausted and emphatically katabolic cells — are male. As Vines 

 says, "the one is passive, the other active ; the former is to be regarded as the 

 female, and the latter as the male reproductive cell." 



4. Further, in another alga (Cutleria) the differentiation may be traced. 

 Two kinds of units result, which must unite with one another if development is 

 to take place, but these units arise from perfectly distinct sources in the parent 

 plant. The larger less mobile cells, which soon come to rest, are fertilized by 

 the smaller more active units. The more anabolic or female cells are fertilized 

 by the more katabolic or male cells, which have now gone too far for the 

 possibility of independent development. 



5- To complete the series, we may simply mention such a case as that to 

 which we shall presently return — those forms of Volvox, where an entire 



