HARD WICKE' S S CIENCE- G O SSIF. 



247 



not widely so ; and if we merely recognise the charac- 

 teiistic features of the two groups we shall find that 

 if, as Haime has done, we divide the genus into 

 single and double, we shall overcome many of the 

 difficulties which beset us in these intricate studies. 



The character upon which Blainville relied in 

 his division of the simple and double types of 

 Diastopora was the lamella which separated the 

 leaf-like growths. In all the Mesenteripora figured 

 by Busk this character is shown. It is not however 

 a unique character for this group alone. The 

 Ptilodictyre of the older rocks have a similar 

 character, and after very closely investigating this 

 feature in the Ptilodictyae and in the Oolitic 

 Mesenteripora, I cannot attach much importance to it 

 in a classificatory point of view. It is well to note 

 the peculiarity, as some systematists may attach 

 importance to a feature like this. In the case of 

 Blainville the foliaceous species occupied a medium 

 position between the Escharoid Adeone and Retepora. 

 The assumption was a false one both in a structural 

 and in a classificatory sense, and for this, if not for 

 anything else, the name ought to be abandoned. 

 D'Orbigny, however, preserved the two divisions, but 

 re-christened one, and to some extent Bi-Diastopora, 

 D'Orb., and Mesenteripora, Blain., are synonymous 

 terms. The foliaceous types were made to do service 

 under other names, such as Elea, and Multelea and 

 Lateromultelea — divisions by no means essential or 

 valuable when endeavouring to establish, in a popular 

 treatise like the present, the probable relationship of 

 the Diastoporid^e. 



The name of one division of this family may well 

 be glanced at here, because it still keeps a place in 

 some of our Natural History hterature, the genus 

 Bercnicca, Lamx. The type of the genus is a 

 Diastopora, the D. diliiviana of the environs of Caen. 

 It comprehended also two living species which 

 cannot be determined by a reference to the illustra- 

 tions of the author. Jules Haime maintains the 

 genus in his work on Jurassic Bryozoa. If we 

 accept the type of Lamouroux we are not bound to 

 accept the genus, for the very simple reason that 

 many diverse forms have been grouped together in 

 accordance with the original blunder of the founder. 

 It is the same with Ceroipora, Gold. It may, 

 however, be essential to retain the name for species 

 of the Diastoporidffi in the Paleozoic Rocks, but 

 that will be considered further on. 



I am not able to speak very critically of the 

 Diastopora of the Cretaceous Rocks. I have, it is 

 true, a few specimens that have been identified with 

 described types, but I have not been able to verify 

 identifications that have been made for me out of 

 kindness. If there be friends living in Cretaceous 

 districts, either foreign or British, who will allow their 

 collections of Diastopora to be examined, I shall be 

 glad to undertake the labour of description, otherwise 

 I shall ;pass on to the Oolitic types, which are 



numerous and well preserved ; and here I find much 

 to compel a student to pause ff only to admire the 

 beauty of the types, or the means by which things 

 so small have been preserved. 



Attcrdiffc, Sheffield. 



[To he continued.) 



NOTES FOR SCIENCE CLASSES. 



{Continued from page 53.] 



Part III. 



IN our last notes we traced the various layers 

 in roots, now let us again briefly refer to the 

 stems in section. Take a branch of the pine, if 

 possible the second year's growth ; our illustrations 

 are from the riniis cxcclsa, a specimen from which 

 may be secured throngh any gardener or public 

 park. First observe the parts, as already worlced 

 out in the lime, and compare with the transverse 

 section of pine stem (fig. 169). 



When cutting any section containing resinous secre- 

 tions, a little methylated spirit should be used on the 

 blade of the razor : this will counteract any unpleasant- 

 ness from its sticky nature. Notice No. I, the bark, 

 a thick layer of cortical ground tissue, containing 

 chlorophyll , with a prominent epidermis on the out- 

 side ; 2, cambium ; 3, second year's concentric layer 

 of woody bundles, or xylem ; 4, first year's xylem, in 

 which are seen resin passages ; 5 is the medullary 

 sheath ; 6, medulla or pith ; 7, one of the medullary 

 rays ; and 8, resin passages in the bark. 



Then, having cut several longitudinal sections, 

 select one as perfect as possible (see fig. 170, longitu- 

 dinal section of pine stem) ; No. i is the cambium; 



2, second year's xylem ; 3, first year's xylem ; 4, 

 medullary sheath ; 5, medulla ; 6, medullary rays ; 

 7, note the starch cells in this portion of the section ; 

 and 8, epidermis. In observing this specimen, care 

 should be taken to understand the resin passages, 

 seen abundantly in the older wood ; it should be 

 examined beneath a high power, when it will be seen 

 to be a large intercellular space or passage, in this case 

 known as a resin passage. (See Sachs' " Text Book," 

 and Thome's "Structural Botany," for exj^lanation, 

 &c.) Also, the xylem in longitudinal section should 

 be submitted to a higher power, to detect the 

 beautiful and characteristic markings, or pitted tissue. 



Whilst the pine is being studied, and during the 

 same lesson, a transverse section of one of the leaves 

 should be made (see fig. 171). Mark carefully the 

 position of the phleum and xylem, respectively ; the 

 numbers refer to : i, epidermis ; 2, ground or funda- 

 mental tissue, or parenchyma, containing chlorophyll ; 



3, bundle sheath ; 4, xylem — this is readily detected, 

 being darker in colour than No. 5, or phleum. 



There are other portions, which play an important 



