32 The Botanical Gazette. [January, 
plants. In this case, Stahl considers that the staying open 
on the part of the stomata has to be accepted as a ‘‘neces- 
sary evil” in order to grow in a substratum that renders the © 
development of other plants impossible on account of the 
closing of the stomata due to the salt. 
IV. Closing remarks. 
The closing remarks of the paper are especially interesting 
because they give more clearly the author’s ideas on several” 
important questions. 
He points out in the first place that the power to open and 
close the stomata has been of great value in the evolution of 
plants, in that it gives them the power to grow ina much 
wider moisture range. Those which have not this power can 
grow only in extremely moist places. | 
He goes on to say that the fact that transpiration repre- 
sents a usual accompaniment of assimilation has been undet- 
stood in different ways. Some look upon it as a necessary 
evil, while others (especially following Sachs) recognize in it 
an important physiological function, whose significance lies 
in the fact that it enables a continuous supply of water con 
taining mineral nutriments, to reach the assimilating cells. 
he opposite opinion has been expressed in a most efm- 
phatic manner by Volkens and is based (in his case) on the | 
astonishingly many sided arrangements for the protection of 
desert plants against loss of water. 
In support of the first idea Stahl states that in numerous 
domestic and especially tropical plants, various arrangements 
exist which can be explained in no other way than that they 
are used in transpiration. Many plants are, of course, able 
to rid themselves of an excess of water in some other way, ® 
by water pores; but still there are many which have no water 
ores. Here it is transpiration alone which carries off the 
water from the leaves and makes room for afresh supply Co™ 
taining nutritive substances. He thinks the importance of 
transpiration may also depend on the fact that it promotes the 
distribution of mineral nutrients. He agrees with Sachs 
sentence that ‘‘the organization of the land plants is only 
comprehensible when we bear in mind the indicated purposé 
of the waterstream.” While inthe desert and prairie plants, 
there are many water-saving devices, on the other hand, 
the shade plants and those growing in the dampest tropical 
3 
eR aa NIBP COB HORN LN APES LENET 
