168 



THE GEOLOGICAL HISTORY OF PLANTS. 



(a) Calamites proper, which has the woody wedges of scalari- 

 form or barred tissue with thin medullary rays, and the thick pri- 

 mary medullary rays are cellular. 



(b) Calamopitus has reticulated or multiporous tissue in the 

 woody wedges with medullary rays, and the primary medullary 

 wedges are composed of elongated cells. 



(c) Calamodendron has the woody wedges of barred tissue as in 

 a, with medullary rays, but has the intervening medullary wedges 

 of an elongated tissue approaching to woody fibre, and also with 

 medullary rays. 



To these I would add a fourth type, which I have described, from 

 the coal-formation of Nova Scotia.* 



(d) Eucalamodendron differs from Calamodendron in having 

 true bordered pores or pseudo-scalariform slit-pored tissue, and cor- 

 responds to the highest type of calamitean stem. 



I would also add that under a and b there are some species in 

 which the woody cylinder is very thin in comparison to the size of 

 the stem. In c and d the woody cylinder is thick and massive, and 

 the stems are often large and nodose. 



As an example of an ordinary Calamite in which the external 

 surface and foliage are preserved, I may quote the following from 

 my report on the " Flora of the Lower Carboniferous and Millstone 

 Grit," 1873 i 



Calamites Undulatus, Brongniart. — This species is stated by 

 Brongniart to be distinguished from the G. Suckovii, the character- 

 istic Calamite of the middle coal-formation, by its undulated ribs 

 marked with peculiar cellular reticulation. He suggests that it may 

 be merely a variety of C. SucJcovii, an opinion in which Schimper 

 coincides ; but since I have received large additional collections from 

 Mr. Elder, containing not only the stems and branches, but also the 

 leaves and rhizomes, I am constrained to regard it as a distinct 

 though closely allied species. 



The rhizomata are slender, being from one to two inches in 

 diameter, and perfectly flattened. They are beautifully covered with 

 a cellular reticulation on the thin bark, and show occasional round 

 areoles marking the points of exit of the rootlets. I have long been 

 familiar with irregular flattened stems thus reticulate, but have only 

 recently been able to connect them with this species of Calamite. 



The main stems present a very thin carbonaceous bark reticu- 

 lated like the rhizomes. They have flat, broad ribs separated by deep 



* " Quarterly Journal of the Geological Society," 1871. 



