364 Origin of Each Species Considered Separately. 



liage behave in the same way.-^ Another striking example 

 is afforded by the decussate arrangement of the leaves 

 of young trees of Eucalyptus Glohidus, a species which in 

 adult life has long-stalked leaves arranged on a different 

 plan.- Siiun lati folium and Berula angustifolia have in 

 adult life simply pinnate leaves but in youth the broad 

 compound leaves which are characteristic of other Um- 

 belli ferae, and therefore evidently are like those of their 

 ancestors. There are numerous other examples^ of spe- 

 cies which exhibit the characters of the systematic group 

 to which they belong as special characters of their early 

 stages. These are the truest cases of atavism. 



The d\NdiVi-0 enothera is another example of a species 

 which behaves in this way. With this difference, that in 

 this case the ancestry is known by direct observation 

 whilst in the other cases it has only been deduced from a 

 comparative study. But the important point is that in 

 this respect 0. nanella behaves as an ordinary species, or 

 rather, what is much more important, that the best sys- 

 tematic species behave in the same way in respect of this 

 form of atavism, as elementary forms which have just 

 arisen from the parent t3^pe. 



It is usually during this "atavistic" stage that the 

 fate of the plant — whether annual or biennial — is de- 

 cided. If the former, the stem begins to be formed al- 

 most immediatel}^ ; the elongate leaves are a kind of prep- 

 aration for this, for the leaves which clothe the lower 

 part of the stem are of this form as is shown in the left 



^J. Reinke, Untersuchungcn iibcr die Assimilationsorgane der 

 Leguininosen, Jahrb. fiir wissensch. Botanik. Bd XXX, Heft I uiid 

 4, 1 896- 1 897. 



^ F. Delpino, Teoria generale dclla HUotassi, Geneva, 1883, p. 242. 



' For the Conifers see L. Beissner, Handhuch der Nadelhoh- 

 kunde, 1891. 



