244 COMPENDIUM OF GENERAL B0TAN7. 



a supply of air and facilitates floating ; the vessels are less numer- 

 ous than in the land-form. This shows that there is a suitable 

 adaj)tability between the external environment and the anatomical 

 structure. Physiology is, however, unable to explain these causal 

 relations. It cannot explain why a locality delicient in water will 

 decrease the intercellular spaces and increase the vascular bundles. 

 We can, however, understand somewhat the suitableness of such 

 adaptation. If we recognize such knowledge as an ex])lanation of 

 the cause, we make an inexact use of the expression, since we pre- 

 suppose something as known which is unknown.' Below we will 

 have more to say about the variation of plant-forms and the effec- 

 tiveness of external and internal causes. AVe will conclude this- 

 chapter with a remark on constancy. 



Nageli" makes a sharp distinction between constancy in the 

 narrower sense {constancy in time) and permanence {constancy in 

 space). What we usually call " constancy " can generally only 

 have reference to space. We compare individuals developed at the 

 same time in different localities. Constancy in time (real con- 

 stancy) is usually not tested by the systematist. This would be 

 done by securing the same species or varieties from different 

 localities and cultivating them for years under the same environ- 

 ment. 



AVe will now discuss the differences between the theory of 

 special creation and the theory of natural descent. 



D. Special Ckeation and the So-called Theory of 

 iJ'ATUEAL Descent. 



The doctrine that the first plant-forms sprang from lifeless 

 matter at the command of the Creator, hence were formed in a 

 supernatural way, is in no wise contradictory to the teachings of 

 natural history. We learn from the book of Genesis (1) that 

 a series of different plant - siJecies were created, (2) that the 

 "earth," hence lifeless matter, brought forth the plants.' Chem- 



1 lu connection with this statement it might be well to remind the student who 

 is inclined toward speculative reasoning that all knowledge, no matter what it may 

 be, is based upon something which is unknown, and which is therefore taken for 

 granted. — Trans. 



'■^ Mech.-physiolog. Theorie der Abstammungslehre, 1884. 



3 It is a (luestionable proceedure for a modern scientist to quote the writings 



