CHAP, xiii EQUISETINEjE 459 



E. scirpoides, to thirty to forty, or even more, in E. telinateia and 

 E. robiistuvi. 



Fossil EquisetinecB 



To this class are usually assigned two groups of fossil 

 plants, one belonging to the Equisetaceae, and represented by 

 the genus Eqiiisetites, which evidently was very close to the 

 genus Equisetum, if not identical with it. The other group, the 

 Calamarieae, differed in some respects from the living forms, and 

 there is much diversity of opinion about their real affinities. 

 The best known members of this order are the Calamiteaj, 

 whose anatomical structure is well known. Cormack ^ has 

 recently made a comparison of the structure of these with 

 Equisetuin, and comes to the conclusion that the type of 

 structure is essentially the same. The general points of 

 difference are the completely separate leaves of the Calamites, 

 the frequent absence of diaphragms at the nodes, and the 

 marked secondary thickening of the vascular bundles. Cormack 

 has shown that a slight thickening of the same character occurs 

 in the nodes of E. maximum, and in the Calamiteas this thicken- 

 ing seems to begin in the nodes and to extend later to the inter- 

 nodes. Cormack concludes that all the Calamitea^ possessed 

 this secondary thickening of the stem. The two groups 

 Annularieae and Asterophylliteai, which have slender stems with 

 regular whorls of leaves at the nodes, have been found to be 

 to some extent, at least the smaller branches, of indubitable 

 Calamiteae ; but it is questionable whether this is always so.- 



The most important remains of this group are the fossils 

 known under the name CalamostacJiys. These are cone-shaped 

 structures, whose close affinity with Equisetum is beyond 

 question. The whorls of sporophylls, which are peltate, like 

 those of Equisetum, and bear four sporangia upon the lower 

 surfaces, are separated by alternating whorls of sterile leaves. 

 Through the kindness of Dr. D. H. Scott ^ I have had an 

 opportunity of examining a beautiful series of sections of C. 

 Binneyana. The structure of the axis and sporangia corre- 

 spond in the closest manner to those of Equisetum, but a 

 most interesting difference is the fact that this genus was 

 heterosporous. Macrosporangia and microsporangia occurred 

 in the same strobilus, but the difference in the size of the 

 1 Cormack (i). - Solms-Laubach (2), p. 323. ^ Scotland Williamson (i). 



