952 



SCIENCE. 



[N. S. Vol. XXI. No. 547. 



tell whether this is a special ease of gametic 

 union in the fungi, or whether similar phe- 

 nomena may be found to be characteristic 

 of other groups where there is gametic 

 union. 



The discovery of IMendel's hybridization 

 studies and the independent confirmatory 

 evidence furnished by de Vries, Correns 

 and others all indicate the necessity of 

 differentiating unit characters and of fol- 

 lowing separately the inheritance of each 

 unit character. The idea which it involves 

 of the purity of the gametes with respect 

 to unit characters, the segregation of unit 

 characters in the formation of the gametes, 

 is one of fundamental importance. Such 

 work has given a marvelous impetus to 

 studies in inheritance. Numerous investi- 

 gators have followed up this work, but it 

 will be many years, perhaps, before a test 

 of the IMendelian laws can be carefully 

 made with any great number of plants and 

 animals. The exceptional instances al- 

 ready reported of the appearance of mo- 

 saic characters and the dissimilarity in the 

 product of reciprocal crosses themselves 

 indicate further fields for experimental 

 research. Only a word need be said bear- 

 ing upon the phylogenetic side of physi- 

 ological work, since phylogeny, as well as 

 pathology or ecology, constitutes a separate 

 section of biological science. The ad- 

 mirable work accomplished by de Vries, 

 serving beyond all question to demonstrate 

 experimentally the origin of species by 

 leaps or mutations, necessitates laying fur- 

 ther stress upon discontinuous variation as 

 a factor in the origination of existing spe- 

 cies of plants. It is to be doubted, how- 

 ever, that most botanists will at present 

 concur in such an opinion as that the evi- 

 dence advanced is sufficient to disregard 

 or disparage the part which is played by 

 continuous variation in the origination of 

 species. Continuous variation must be 



manifest by relatively .slight variations; 

 and it would be unfair to expect at this 

 time the experimental proof of its eflS- 

 ciency. It may even be assumed that there 

 is a complete series between continuous 

 variations and discontinuous variations, as 

 Avell, perhaps, as between the possibilities 

 of inheriting immediately or ultimately 

 such variations. Many of the problems in 

 plant physiology are distinctly practical 

 problems. The task of the physiologist is 

 primarily to study the activities of plants 

 irrespective of practical bearing. To have 

 the greatest possible breadth and force, 

 however, the cultivated plant may not be 

 neglected in any of its artificial environ- 

 mental conditions. It is unfortunate that 

 as yet physiological botany has not been 

 made fundamental to agronomy, horticul- 

 ture, forestry and other sciences, arts or 

 commercial pursuits. Physiology can not 

 be limited by any practical problems, nor 

 can any sacrifices be made, but a sympathy 

 with commercial endeavor will invigorate 

 the work, will afford equipment and will 

 contribute towards the common good. 



In conclusion, it may be said that pres- 

 ent-day physiology, even more than any 

 other section of biological science, is funda- 

 mental. Many phases of pathology, ecol- 

 ogy, phylogeny and experimental morphol- 

 ogy, especially, may not be clearly differ- 

 entiated as sections. Broadly conceived, 

 plant physiology concerns itself : 



1. With the relationships of existing or- 

 ganisms, ontogenetically and phylogenetic- 

 ally. Phylogeny would necessarily claim 

 much of this general field, as would also 

 morphology, ecology and other subdivi- 

 sions. 



2. "With the functions or activities of 

 organs, tissues and cells, and the interac- 

 tions and interrelations of these one with 

 another and with external forces. It is 

 here that morphology touches physiology 



