504 
NATURE 
[ Oct. 26,1871 

was remarked that during its perpendicular fall to the horizon it 
gave out vivid scintillations. 
It is difficult, from the exaggerated language of native narra- 
tives in the East, to suppose that the destruction of life and 
property described, from the Zimes of /ndia, as an unprecedented 
catastrophe in Sind, in the next paragraph of NATURE, was 
occasioned by an unusual fall of meteorites. In the absence of 
fC REFERENCE NUMBERS. + 
12345 67 8 9.10l 12131415 16 17 1819 
i y 
2 cS 3 8 
a 
Heicut 1n British Statute MILES ABOVE THE SEA-LEVEL. 
iy 
2, etl 2 a 

HEIGHTS OF LWENTY SHOOTING->XTARS DOUBLY OBSERVED AT EIGHT 
BRITISH ASSOCIATION STATIONS IN ENGLAND ON THE NIGHTS OF THE 
QTH TO 12TH OF AUGUST, 1871. 

any evidence that a loud report, and other aérolitic phenomena 
perceived at a great distance, accompanied the occurrence, its 
unusu-lly disastrous effects may rather, doubtless, be ascribed to 
devastations produced by lightning of extraordinary violence. 
On the accompanying diagram the real heights of some shoot- 
ing stars are represented which were simultaneously recorded by 
observers of the annual meteor-shower in August last, at eight 
British Association stations in England. A. S. HERSCHEL 
Newcastle College of Physical Science, Oct. 16 
Exogenous Structure in Coal-Plants 
PROF. WILLIAMSON criticises my want of certainty with respect 
to the exogenous mode of growth of extinct Lycopodiacez. But 
surely his reference to the Dixonfold trees does not prove more 
than that the diameter of their stems was greater near the roots 
than higher up. The same thing is true of many palms, but I 
think Prvf. Williamson would be the last person to say that 
it was evidence of ¢heix being exogenous. Nevertheless, as I 
have already said, I am inclined to think that Prof. Williamson 
is right in supposing that the stems ot extinct arborescent Lyco- 
podiaceze increased in thickness, although I do not see my way 
to asserting off hand that this was the case. Even admitting, 
with all Prof. Williamson’s confidence, that it was so, I can see 
no classificatory value in the fact to justify overriding reproductive 
characters in his new classification. 
I said in my former letter (and the argument still appears to 
me a good one) that this increase was in any case ‘‘ nothing 
more than an adjustment to an arborescent habit dropped when 
the arborescent habit was lost.” Prof. Williamson finds some 
difficulty in understanding this, and believes me to imply ‘‘ that 
these exogenous conditions were merely adventitious growths 
assumed fur a season and thrown off at the earliesr opportunity ; 
that they had no true affinity with the plants in which they were 
found.” He confesses that he sees no ground for so remarkable 
a conclusion, and I may certainly say that as faras I comprehend 
it, neither do I. 
What I did mean to imply was, that in comparing the stems 

of existing with those of extinct Lycopodiacez, allowance must 
be made for such adaptations of structure as would be likely to 
be correlated with enormous size. To make the matter clearer 
by an illustration :—Suppose we compare a nearly allied woody 
and herbaceous plant, say a lupin and a laburnum, we shall 
find in their stems (both ‘‘exogens”’) the same kind of diffe- 
rences as exist between the stem of a herbaceous Se/aginel/a and 
that of the nearly allied arborescent Lefidodendron. Yhe lupin 
may have had arborescent ancestors ; if so, it has dropped ail 
such adaptations of the structure of its stem to an arborescent 
habit as we find existing in laburnum. Assuming (what is of 
course o7/y an assumption) that Se/aginella is a descendant of 
Lepidodendron or its allies, the parsimony of nature has also sup- 
pressed in it all those peculiarities of stem structure which were 
merely correlated with vast size, and in Sv/aginel/a and recent 
Lycopodiacee we have the residuum. In Jsoetes, which is only a 
few inches high, there is a kind of lingering reminiscence of cir- 
cumferential growth. 
Prof. Williamson says that ‘‘herbs if they belong to the 
exogenous group are as truly exogenous in their type as the most 
gigantic trees of the same class. Size has nothing to do with 
the matter.” With these statements I altogether disagree. I 
look upon the terms exogen, endogen, and acrogen as alrogether 
obsolete from a classificatory point of view. Mohl pointed this 
out more than twenty years ago. Compare the following re- 
marks from one of his memoirs with Prof. Williamson’s: ‘* The 
course of the vascular bundles in the palm stem and in the one- 
year-old shoot of the dicotyledons is exactly similar, and the 
conception of a different mode of growth, and the division of 
plants into endogens and exogens formed on it is altogether 
opposed to nature.” 
Size, in fact, has everything to do with the matter. Itis the 
persistent growth of the ends of the branches which makes the 
strengthening of the main stem by circumferential growth a 
mechanical necessity. Palms not being branched do not require 
the voluminous stem of an oak, and they exhibit on an enlarged 
scale only the structure of a one-year-old herbaceous shoot. 
But in the dragon-tree of Teneriffe an ‘‘endogen,” which 
becomes extensively branched, there is a true circumferential 
growth of the main stem, which increases far? Aassiz with the 
development of the branches. All herbaceous stems, on the 
contrary, among flowering plants, whether belonging to the 
exogenous or endogenous group, have practically the same type 
of structure. Where is the exogenous type in the stem of the 
common artichoke, or in /vrula communis, figured by De 
Candolle in his ‘‘Organographie Végétale,” pl. 3, fig. 3, 
** pour montrer a quel point elle simule les tiges de mono- 
cotylédones” (endogens) ? 
I think these remarks make it plain that circumferential (which 
is a preferable expression to exogenous) growth in stems is simply 
a necessary accompaniment of a branched arborescent habit. 
As far as the affinities of plants are concerned, it is purely acci- 
dental and of no classificatory value. Zzfines being herbaceous 
and Laburnum arborescent does not prevent their being placed 
in the same tribe of a natural family. Since Mohl has shown 
that one-year-old (herbaceous) stems conform to the endogenous 
type, while such woody stems as Ladbwrmum possesses are of 
course exogenous, it is clear that Prof. Williamson’s views would 
overthrow all the work of modern systematists, and bring us back, 
as I pointed out in my former letter, to the primitive division of 
plants into trees and herbs (not trees and sirwés as Prof. Wil- 
liamson makes me say). 
‘The interpretation of the actual structure of the stems of the 
extinct Lycopodiacez is of course another matter. Prof. William- 
son illustrated his views at Edinburgh by referring to Lepidoden- 
dron selaginoides ; every botanist who took part in the discussion, 
however, objected to his explanation. It may be true that this 
is only one form of such stems, but of course I can hardly be ex- 
pe-ted to be acquainted with the unpublished material which 
Prof. Williamson still has in hand. There is, I think myself, 
good reason for believing that Lefidodendron, Sigillaria, and 
Ulodendron all belong to a common type of stem structure ; 
differences in fragments of different age of growth must be ex- 
pected and allowed for. Of course, as I do not accept the 
existence of a pith in these plants, the pith or medullary rays 
must be rejected as well. Mr. Carruthers has shown, I think, 
conclusive reasons for disagreeing with Dr. Hooker with respect 
to the spaces which he identified with those structures. I was 
already familiar with the view of these s'ems taken by Prof. 
Williamson in his last paper. Those who are interested in the 
matter must judge for themselves who is right. 
