ORCHID CONFERENCE. 



405 



stiiiiuius may be imparted to the egg-cell artificially and without the 

 aid of the male gamete. 



For example, Loeb has demonstrated that, if the egg-cells of sea- 

 urchins be taken from the parent and placed in sea-water free alto- 

 gether from male cells, an alteration either of the composition or 

 concentration of the sea-water suffices to cause the egg-cells to develop 

 into embryos. Nature herself provides us with illustrations of a similar 

 phenomenon in the case of parthenogenetic plants. Species of 

 Hieracium, Alchemilla, Taraxacum, and other plants are known to 

 give rise to good seed even though the egg-cells be not fertilized. 

 Similar examples of the parthenogenetic development of eggs into 

 embryos are known among various kinds of animals, and particularly 

 in insects — for instance, in the summer broods of aphides. 



In parthenogenetic plants and animals the egg-cells carry, as it- 

 were, their own stimulus to development; or, rather, the egg-cells oi 

 such plants differ from those of the majority of organisms in that they 

 retain the power of development, and are not compelled to await the 

 advent of the male gamete in order to resume their growth. Even 

 more remarkable than the chemical embryos just described are the 

 mechanical embryos which have been produced recently by Bataillon. 

 This experimenter removed the ripe, unfertilized eggs from the frog, 

 punctured each egg by means of a fine glass needle and covered the 

 eggs with water. Of the punctured eggs many died, but out of 1000 

 which were operated upon no fewer than 120 hatched into tadpoles and 

 actually reached the stage at which the legs are developed and the tail 

 is disappearing. 



Astonishing and well-nigh incredible as are these facts, they are 

 attested so well that they must be accepted. They are,, moreover, 

 susceptible of interpretation in terms o'f the hypothesis at which we 

 have arrived already. The needle-puncture sets up a disturbance in 

 the egg-cell, the effect of which is similar to that exerted by the 

 i entrance of the male gamete into the egg-cell. In either case, growth 

 1 and division occur, and the embryo is produced. Needless to say, a 

 ■ tadpole begotten in this manner constitutes a novel and absolute kind 

 i of orphan — namely, one that never had a father. It can possess 

 maternal characters only. 



Finally, it may be mentioned that Delage and others have sue 

 j ceeded in raising larval animals (Echinoderms) by fertilizing egg-cells 

 I deprived of their nucleus by normal male cells. Such larvae have 

 I nuclear material of paternal origin only, and on current hypothesis they 

 should exhibit paternal characters only. 



We are now in a position to state with clearness the significance 

 i of fertilization. By the fusion of the nucleus of the male and female 

 j gametes parental characters are transmitted to the offspring; by the 

 { entry of the male cell into the egg-cell the latter is provoked or 

 I stimulated to 'form the embryo. The stimulation is of a chemical or 

 mechanical nature, and may be brought about by artificial means. 

 That these conclusions apply also to plants there can be no doubt, 



