SIGNIFICANCE OF THE SEXUAL PROCESS. 49 



From our present state of knowledge of the development of the 

 blepharoplast there is but one conclusion, it seems to the author, that 

 can be legitimately drawn concerning their origin, namely, that they 

 arise de novo. As regards centrosomes the evidence is more compli- 

 cated and conflicting. Although, in the opinion of the author, the 

 evidence is decidedly against the doctrine of the genetic continuity of 

 the centrosome, yet the proof is not quite conclusive. If centrosomes 

 also arise de novo, then the problem assumes a slightly different aspect, 

 for it is questionable whether we are justified in speaking of homologies 

 between organs that, as such, are without genetic continuity. 



There is strong evidence, which seems to be increasing from day 

 to day, that it is the fundamental substance known in the plant cell as 

 kinoplasm which is genetically continuous. After a careful considera- 

 tion of the facts, the author is led to the same conclusion concerning 

 the centrosome to which he gave expression in 1900, in a paper on 

 the nuclear division in Dictyota (1. c., p. 178), namely, that it is the 

 kinoplasm which should hold the rank of morphological unit, and that 

 the centrosome should be regarded as an individualized part of the 

 same, existing in that form in some organisms and not in others, for 

 reasons that cannot at present be explained. As regards blepharo- 

 plasts, about the only conclusion in harmony with all the facts is that 

 these bodies represent individualized parts of the kinoplasm which 

 arise de novo in certain spermagenous cells, and from which the cilia 

 are developed. 



SIGNIFICANCE OF THE SEXUAL PROCESS AND THE NUMERI- 

 CAL REDUCTION OF THE CHROMOSOMES. 



Speaking generally, the phenomena resulting from the sexual process 

 fall into two categories, namely, (i) the transmission of hereditary 

 characters, together with the blending of two lines of descent by the 

 fusion of the sexual nuclei, and (2) the imparting of a growth stimulus 

 to the fecundated egg or to the zygote, by which the energy of growth 

 and division is restored. 



Correlative with the first category is the reduction in the number of 

 chromosomes. The doctrine of the significance of the numerical 

 reduction of the chromosomes now generally accepted by botanists as 

 a working hypothesis, was first stated in a well organized form and 

 presented formally to botanical science by Strasburger ('94) in a mas- 

 terly essay on the " Periodic Reduction of Chromosomes in Living 

 Organisms." The enunciation of this doctrine marked the beginning 

 of a new epoch in the study of sexuality and in cytological research in 

 plants. 



