Feb. 20, 1873}. 
of the Root.” Dr. Frank “ On the position and direction 
of floating and submersed parts of plants.” Dr. Cohn 
“On Parasitic Alge.” Dr. Schroeter “On certain 
Pigments formed by the Bacteria,” and Dr. Cohn’s 
‘Investigations on Bacteria.” a. 
This work—Cohn’s “ Beitrage zur Biologie der Pflanzen” 
—is the organ more especially of the workers in the phyto- 
physiological laboratory at Breslau, under the guidance 
of the eminent Professor of Botany in the University 
o) The first part appeared in 1870 (NATURE, vol. iil. 
. 242). 
P Dr. Ciesielski’s researches follow up the interesting 
inquiries into the same subject opened a few years ago. 
by Prof. Hofmeister and others. He sums up with the 
following propositions :— 
1. The normal growth of germinating seedlings may be 
observed in a saturated atmosphere, ifthe albumen or 
cotyledons be kept constantly moist, without the root 
descending into either water or moist earth. The de- 
velopment of the root ceases however as soon as the 
reserve of nutrient matter in the seed is exhausted. 
2. The longitudinal extension of the root takes place 
exclusively in a relatively narrow region behind the tip. 
3. The downward curvature of the root takes place at 
that point where the longitudinal growth of its cells is at 
a maximum. 
4. Gravitation occasions the downward curvature. 
5. This curvature is not passive but active; that is to 
say, gravitation occasions in the root a tension of the 
tissue whenever it departs from its normal direction, and 
thus determines downward curvature. 
6. This tension is due to the more considerable growth 
of those cells which lie on the side of the root turned 
towards the zenith. 
7. The more marked growth of the cells of this side of 
the root is occasioned by the circumstance that the cell- 
contents of the upper side turned towards the zenith are 
much less concentrated than in the under side ; which, 
again,is due to the action of gravity which determines 
that the more concentrated cell-sap, being the heavier, 
shall occupy the under side of the root. 
8. If the outermost tip (Vegetationskegel) of a root be 
cut off, it may indeed elongate through mere extension 
of its tissues, but it is no more capable of downward cur- 
- vature. 
9. If however it afterwards developes a new formative 
apex, as occasionally happens, and so elongates at the 
cut apex, the root again becomes capable of downward 
curvature. 
1o. Centrifugal force determines in a similar manner 
and on ana'ogous ground, the curvature of the root in the 
direction of this force, as does gravitation in that towards 
the nadir. 
The next thing will be to explain the relation of 
ascending axes to gravitation. It would seem as though 
heliotropismus and geotropismus had squabbled over the 
embryo and compromised matters at last by each taking 
a Vegetationskegel, one of the plumule the other of the 
radicle, with its active future contro! ! 
Dr. Frank’s paper is an inquiry into the causes which 
influence the position and direction of the floating and 
submersed leaves of aquatic plants apart from the direct 
operation of gravity and sunlight, which are not causes 
directly produc ive of special modifications of growth, but 
rather guides accorcing’ to which the organ in the course 
of growth adjusts itself so far as itis able, until it has 
attained a position the most advantageous to it. 
Prof. Cohn’s memoir touches upon the question, of 
peculiar interest just now, of the relation of the lower 
forms of vegetable life destitute of chlorophyll to the 
organic matter in which they find their matrix and to the 
inorganic world, with regard to their power of assimilating 
independently their necessary nutriment and reducing 
carbonic acid. He also carefully describes as a new 
NATURE s01 
unicellular genus of truly parasitic alge, Chios ochytrium 
(allied to AHydrocytium and the Chytriding) which he 
finds inhabiting the fronds of Lemna trisulca. The 
occurrence of this chlorophyll—containing alga in Lemna, 
he regards as presenting an analogy with the presence of 
the green gonidial layer in lichens, which he looks upon 
similarly as an endophytal alga. 
LETTERS TO THE EDITOR 
[The Editor does not hold himself responsible for opinions expressed 
by his correspondents, No notice is taken of anonymous 
communications. | 
The Janssen-Lockyer Application of the Spectroscope 
I sEE by a letter in the Zxglish Mechanic and World of 
Science of January 31, that Mr. R. A. Proctor claims for Dr. 
Huggins the credit of having publicly described in Feb. 1868, 
the method of viewing the solar protuberances without a total 
eclipse. 
Permit me to state that to Mr. Lockyer undoubtedly belongs 
the credit of having known this method even before his preli- 
minary paper in 1866 in which it was sufficiently published. 
We had numerous. conversations on the subject, and when he 
showed me the MS. of his preliminary paper and told me at 
the same time that he was about to ask a grant for the purpose 
of procuring a more powerful spectroscope, I advised him to 
introduce his views in the shape of a question, which he accord- 
ingly did in the following terms :—‘‘ May not the spectroscope 
afford us evidence of the existence of the ‘red flames’ which 
total eclipses have revealed to us in the sun’s atmosphere, 
although they escape all other methods of observation at 
other times? and if so may we not learn something from this of 
the recent outburst of the star in Corona?” 
I gave this advice to my friend, Mr. Lockyer, because I thought 
that as it might be some time before he obtained the new instru- 
neit it might be well thath: should publish what Ifconceived 
would enable him to claim for himself the knowledge of this 
principle. And I think that anyone well acquainted with 
spectra on reading the question put, could not fail to see what 
was meant, and if he were previously ignorant of the principle, 
he could not fail to perceive it. I therefore feel rather astonished 
that anyone should claim the statement made by Huggins two 
years afterwards as being the commencement of a new principle. 
The method founded upon this principle was first successfully 
applied by Messrs. Janssen and Lockyer, acting independently of 
each other, in the year 1868. Mr. Lockyer had by this time 
obtained his improved spectroscope, and the very first day he 
used it he made the discovery. I do not think there is any 
reason to suppose that Mr. Lockyer was at all aided, as was sug- 
gested by Mr. Huggins, in detecting these lines by the somewhat 
vague information of what had been done at the total eclipse in 
India. He was now provided with an instrument capable of show- 
ing these lines to a child—made in fact for the purpose of showing 
them. Now what wouldhave beenthoughtof any one of the Indian 
observers if during the few minutes of a total eclipse he had 
failed to detect the existence of bright lines? Can we imagine 
therefore that an intelligent observer like Mr. Lockyer, with an 
instrument constructed for the purpose and with unlimited time 
at his disposal, should have failed in detecting such lines even had 
he not previously been sure that they existed? I confess I cannot 
understand any observer failing in a thing of this nature, and 
therefore I do not know well how to account for the somewhat 
puzzling remark made by Dr. Huggins in his notes to Schellen’s 
** Spectrum Analysis” as follows :— 
“Though to Mr. Lockyer is due the first publication of the idea 
of the possibility of applying the spectroscope to observe the red 
flames in sunshine, as a matter of history it should not be passed 
over that, about the same time, the same idea occurred quite 
independently to two other astronomers, Mr. Stone of Green- 
wich, and Mr. Huggins. These observers were however un- 
successful in numerous attempts which they made to see the 
spectra of the prominences, for the reason probably that the 
spe:t o cope wh c : they employed’was not of sufficient dispersive 
power to make the bright lines of the solar flame easily visible. 
When the position of the lines was known, Huggins saw them 
instantly with the same spectrosc pe (two prisms of 60°), which 
he had previously used in vain.” 
I confess I cannot yet understand why a distinguished observer 
