DEVELOPMENT AND REPRODUCTION 33 1 



If the word hormones is substituted ior ferments in this sentence the statement 

 becomes quite modern. Many phenomena of growth and of the developmental 

 configuration of plants will surely be found to be dependent upon various hor- 

 mones, and one of the main problems of future investigators will doubtless deal 

 with these internal secretions of plants. 



In recent years proof of the unity of all living organisms and their common 

 genetic origin has repeatedly been adduced from physiological studies. Related 

 organisms generally contain characteristic substances that are chemically 

 related. Studies on animals have given important results in this connection. 

 For instance, repeated injection of foreign blood into living rabbits leads to the 

 formation of a special precipitin or antiserum in the rabbits' blood, and this 

 precipitin produces coagulation in blood of the kind injected. 1 When rabbits' 

 serum, taken from an animal thus treated, is added to the blood of other animals , 

 the latter blood is coagulated only when these animals are of the same species as 

 the animal from which the foreign blood originally came, or when they are closely 

 related to that animal. Blood of species not thus closely related to the animal 

 furnishing the injected blood, is not affected. The antiserum obtained by 

 injecting human blood into an animal precipitates only the blood of man and of 

 the closely related anthropoid apes (the gibbon, orang-outang, chimpanzee and 

 gorilla) while blood of the apes of the new world is not thus coagulated. ' The 

 antiserum produced by the blood of a member of the genus Canis(dog) coagulates 

 blood of other species of this genus but not that of the less closely related beasts 

 of prey. Similar results have been obtained also in plants. Rabbit serum 

 from an animal that has been injected with yeast extract, precipitates extract 

 of yeast and that of truffles, but not that of ordinary mushrooms. It therefore 

 follows that yeasts and truffles are members of the same group of fungi (Asco- 

 mycetes). Experiments of this kind with seed-plants show that injection, into 

 an animal, of extracts of different parts or regions of the same plant, causes the 

 formation of the same antiserum. 



§3. Reproduction. — The physiology of plant reproduction has been very 

 little studied, but it is clear that this process is dependent upon both external 

 and internal conditions. The alga Vaucheria, for example, consists of a long, 

 unicellular filament that reproduces both sexually and asexually. In asexual, 

 or vegetative, reproduction the terminal portion is separated from the remainder 

 of the filament by a dividing wall. The cell thus cut off is the zoosporangium, 

 from which the zoospore escapes as a many-ciliated, motile cell. After a 

 period of free movement, this cell enlarges and grows into a filament like its 

 parent, thus forming a new individual. The process of zoospore formation is 

 markedly influenced by external conditions, as has been shown by Klebs. 2 

 Vaucheria may be grown indefinitely without forming zoospores, or zoospores 

 may be produced at any time, according to the desire of the experimenter. 

 Zoospores never develop when the cultures are kept in moist air, but the filaments 



1 Seber, M., Moderne Blutforschung und Abstammungslehre. Frankfurt a. M., 1909.* Ballner, Franz, 

 Ueber die Differenzierung von Pflanzlichem Eiweiss mittels der Komplementbindungsreaktion. Sitzungsber. 

 (math.-naturw. Kl.) K. Akad. Wiss. Wien ng lrl : 17-58. 1910. 



- Klebs, 1896. [See note 1, p. 300.] 



