320 
Studies of this kind have barely begun. 
Kahlenberg and True were the first to estab- 
lish the poisonous action of ionic hydrogen 
in solutions of certain acids and salts. <A 
few other observers have attacked similar 
problems, but the field is hardly yet ex- 
plored ; it has not been at all cultivated. 
The relations are complex, it is true, and 
their unraveling will not be easy ; but surely 
there are rich harvests for the patient 
worker. 
In the light of the modern theory of so- 
lutions, it is essential that the whole field 
of root absorption be reexamined. Dilute 
solutions of the soil must surely be electro- 
lytically dissociated in large measure, and 
this fact doubtless stands in intimate rela- 
tion to the entrance of solutes into the 
plant. In the absence, at present, of com- 
plete experimental demonstration of the be- 
havior of these substances, we are compelled 
to rely largely upon theoretical probabilities. 
Interesting possibilities, however, present 
themselves to the speculative worker and 
point out various directions in which inves- 
tigation may be fruitful. 
Energy.—One of the directions in which 
physical knowledge is now extending, but 
in which it is still so imperfect as to leave 
much to be desired, is in the understand- 
ing of the forms and transformations of en- 
ergy. But the physiology of plants has not 
yet made use of all the knowledge that is 
available in this direction. Though in the 
past decade we have had some important re- 
searches, there yet remain great gaps in our 
knowledge of the income of energy to the 
plant and of the ways in which it is util- 
ized. I may here indicate only a few of 
these gaps in our knowledge. 
While it is easy to calculate the potential 
energy of the foods absorbed it is not easy 
to determine how much of the energy is 
available, in what form it is released and 
what changes it undergoes, as it is used by 
the plant. 
SCIENCE. 
[N. S. Vou. X. No. 245. 
We know that heat is one form of energy 
which is constantly affecting the organism, 
and we speak of certain temperature limits 
as one of the essential conditions for life. 
But what does that mean? Why is it a 
condition of life? Is it merely because the 
necessary chemical changes can only occur 
within certain limits? If so, what does 
this mean? Does it mean that the radiant 
energy which imparts to us the sensation of 
heat must be acting upon the molecules of 
the various chemical compounds ere they 
are capable of enough lability to afford the 
living protoplasm opportunity to push them 
over, so that they fall into simpler com- 
pounds, or to lift them to a higher level of 
complexity and to greater instability? If 
heat does not merely increase chemical in- 
stability, is life possible within certain lim- 
its of temperature because there is pouring 
into the organism a supply of energy which 
the protoplasm may utilize in directer fash- 
ion to do the work necessary to existence? 
What is the source of energy for the col- 
orless plants which assimilate the simpler 
foods? It is almost inconceivable that they 
can produce proteids ont of the carbohy- 
drate and nitrogen compounds with which 
they can be supplied without needing a con- 
siderable amount of energy besides the po- 
tential energy which reaches them in the 
foods they absorb. If there is no direct 
supply of radiant energy, it looks very 
much as though these plants had acquired 
the long-sought power of lifting themselves 
by their own boot straps. Yet if radiant 
energy, either as light or heat, is utilized 
by them, we know nothing of it at present. 
Or is it the energy of the O, absorbed for 
respiration which accounts for the extra 
work done? The data are not at hand to 
determine the correct answer to these ques- 
tions. General statements abound, and to 
many it may seem that all this is known, 
since it is often dogmatically settled in 
text-books. Yet in reality we must have 
