3 oo 



CALAMARIEAE. 



primary ray. The lacunae in the tissue, expressly mentioned by Renault, 

 are also described by Unger 1 . In Petzholdt's figure these lacunae alternate 

 with other broader passages, which are in all cases placed where the primary 

 ray passes into the pith. They appear to answer rather to incidental gaps, 

 fissures in the tissue, such as are found in this situation in the wood of 

 many Calamitae. It is plain from the above incoherent and imperfect 

 statements how necessary it would be to procure a connected examination 

 of all the material stored up in the Museums. 



The forms grouped together under the name Arthropitys also show 

 many variations in respect to the behaviour of their primary rays (Fig. 39), 

 and these variations may hereafter give rise to the formation of new genera. 

 But at present little has been done in this direction ; a more extended ana- 

 tomical investigation of these woods has still to be made. I must therefore 

 content myself with a reference to the few figures of transverse sections of 

 Arthropitys which the literature supplies. In all of these we find that the 

 primary rays project distinctly where they unite with the pith, and give it 

 a stellate toothed outline, and that towards the outside they either gradually 

 or quite suddenly become indistinct, their tissue approximating in character 

 to that of the wedges of wood. In the former case this appears to be 

 brought about either by the formation of numerous narrow interfascicular 

 strands, an example of which will be found in Williamson 2 , or by gradual 

 increase in breadth of the wedges of wood at the expense of the rays 

 (Fig. 39 C), as is shown in Williamson's 3 and Weiss' 4 figures. On the 

 other hand there are cases in which the entire tissue of the medullary rays 

 in the secondary growth assumes the character of wood after the manner 

 of some herbaceous plants, Labiatae for example and Scrophulariaceae 

 (Fig. 39 B), as appears from figures in Weiss 5 and Williamson 6 ; but the 

 character of the wood, almost unknown, will have to be further inquired 

 into. How far all the differences here indicated are sharply distinguishable 

 from one another, or are connected together by intermediate forms, the 

 meagre material afforded by the literature in the absence of personal in- 

 vestigations of any extent does not enable me to determine. 



Archaeocalamites (Bornia) radiatus also, which will have to be con- 

 sidered more in detail presently, shows similar structure of the wood, as 

 appears especially from Renault's 7 recent descriptions. He has found 

 portions of silicified stems with the characteristic striation in the porphyry- 

 tuffs of Enost north of Autun. A broad pith is surrounded by a closed 

 ring of wood, and the well-known lacunae are found in the primary bundles. 

 The tracheides bear three rows of bordered pits, and the cells of the 



1 Petzholdt (1), t. 8, f. 6. 2 Williamson (1), I, t. 25, ff. j6, 17. 3 Williamson (1), 



I, t. 27, f. 26. * Weiss (5), p. 10, ff. i, 2. * Weiss (5), p. 10, f. 3. 6 Williamson 



(1), I, t. 24, f. 15, and t. 25, f. 20. 7 Renault (19). 



