284 MR. A, В, HORWOOD ON CALAMITES SCHÜTZEI, ETC. 
The second internode again in all but one case (where it is 1-4 em.) is 1:5 em. 
The third varies from 1:9 to 2:5 ст., the fourth from 2-2 to 3 em., and so on. 
Thus in these six specimens gathered at random the two points remarked in 
the extinct Calamitina Schiitzei, Stur, are also to be seen, viz., uniform length 
and position of a short internode, and gradual uniform inerease in the length of 
succeeding internodes, from below upwards. The same remarks as to increase 
apply equally to the leaf-sheaths, and though amongst Calamites we have no 
chance of comparing them, yet in Æquisetites they are usually quite as 
uniform*. Not only is it remarkable to find these characters common to 
Carboniferous and present day groups of the same genetic series, but it may 
further be found to obtain generally in living Æquiseta amongst species living 
under very varied conditions with diverse habit. The table on p. 285 
illustrates this fact. Thus these characters serve as a further means of 
tracing to а common origin the extinct Calamarieze and the living Equise- 
taceæ, now grouped together in a common phylum Equisetales. 
In Equisetum maximum, Lam., in branching stems a gradual deerease in 
the length of internodes upwards, the largest at the base, takes place, whereas 
in fertile stems the converse holds, except in the case of the short internode 
preceding a сопе. When a stem bears both cones and branches the two modes 
of elongation alternate. This is seen in E. pratense, Ehrh. In E. sylvaticum, 
Linn., the same feature is noticed in specimen А f and in С, but in В, in the 
branching period, there is an inerease and then a deerease, three sheaths over- 
lapping. In D the internodes increase up to the node preceding the branch- 
bearing node, then ап internode doubtfully shorter intervenes, followed by a 
regular decrease in length upwards. 
In the var. capillare the elongation is as in А and С of the iype. The 
hybrid between Æguisetum arvense and E. limosum (E. litorale) exhibits a 
little variation, two internodes before the branch-bearing node decreasing, 
not one, but the eighteen succeeding internodes exhibit a remarkably uniform 
normal decrease at the rate of 1 millimetre approximately. In Æ. limosum, 
Linn., var. Лиме ( Linn., sp.), the internode before the br anch-bearing node 
is not shorter than the penultimate one. But after this the length of the 
internodes decreases from the second member of the branch- -bearing period. 
In Æ. hyemale, L., there is a gradual increase in length up to the last one, but 
as the specimen is incomplete it does not serve for comparison. 
* Where any abnormal variation in length occurs either in the internodesor the leaf-sheaths 
it may be reasonably regarded as due to variation in the external conditions or environment, 
amount of light, moisture, etc. 
T In internode 10 there is an abnormal increase, otherwise the sequence is normal. 
