262 de Fr aine . — The Morphology and Anatomy of the 
the radius of the stele, van 
Ufford invariably found that in closely related 
plants the more mobile the station the greater the 
proportion of collenchyma 
developed. Two examples 
will suffice to indicate this fact : 
Habitat. 
Plant. 
Thickness of collenchyma 
radius of the stele. 
^Mobile stones 
Galium helveticum 
1 
i *5 
,, 
Less mobile earth 
,, rotundifolium 
1 
4*3 
Fixed earth . . 
,, verum 
1 
6*o 
Mobile stones . . 
Cerastium lati folium 
1 
i *9 
2.- 
Less mobile earth 
,, arvense 
1 
2*5 
Fixed earth . . 
,, cuneifolium 
I 
5 *° 
He further found that only species which have abundant stereome 
can survive the thrust of the stones ; those which do not possess it die out. 
Starr 1 in an examination of the anatomy of dune plants came to 
somewhat similar conclusions, for she found that comparing the stem of 
a plant from a mesophytic situation with one of the same species from 
the dune, the following characters occurred in the dune form : 
1. The vessels were more numerous but smaller, the total area being, 
however, larger. 
2. The lumen of the fibres was smaller. 
3. The walls of the vessels and fibres were heavier. 
4. More sclerenchyma and collenchyma were developed. 
5. Slight increase in cork formation occurred. 
Finally, Haberlandt thinks that mechanical influences, if they do not 
pass beyond a certain limit, act on the stereome as a stimulus for further 
building it up. 
An examination of the roots of the various forms of S', binervosa 
from the different habitats shows certain constant differences to obtain : 
Annual growth rings. The annual growth rings in the root of the 
Main bank plant are always wider than in those of a lateral plant ; this 
is probably in accordance with the less rigorous conditions to which the 
Main bank plant is subjected. Starr also found a similar relation be- 
tween plants growing in a mesophytic situation and those growing on 
a sand dune, and she states, ‘a majority of xerophytic forms have more 
growth rings to the given diameter than the mesophytic forms, showing 
slower growth under the more adverse conditions.’ 
Wood parenchyma. Development of wood parenchyma is entirely 
absent in the plants from the Main bank and the narrow and the broad 
1 Starr, A. M. : Comparative Anatomy of Dune Plants. Bot. Gaz., 1912, vol. liv, p. 263. 
