Oblique Wall Research Articles

STUDIES ON MARINE BRYOZOA. X. HIPPADENELLA CARSONAE, N. SP

1. The morphology of Hippadenella carsonae, new ectoproct from the Antarctic, is described in detail and measurements made of many of its structures.2. At the time of its collection, Jan. 29, ovicells were empty of embryos but developing eggs were in the ovaries. Developing embryos were absent from the body cavity also.3. Living polypides occurred at the tips of some twigs hut most of the material was dead or empty of polypides, at the time of collection.4. The species has an unusually well developed avicularial apparatus consisting of large glands, reduced polypide, abductor and adductor muscles.5. So-called "oral" or "sub-oral" gland are present. They are near the operculum but have no actual connection with, or proximity to, the true polypide mouth.6. The function of "oral" glands, avicularial glands and avicularial polypide is unknown in this species, and a matter for speculation in other species.7. Other peculiarities of this species are the oblique tubular frontal wall channels (frontal pores) and the mode of secondary calcification where trabeculae span the orifice and a domed lamina seals the ovicell.

Transition processes in shock wave interactions

This paper is a discussion of recent experiments in shock-wave refraction which have clarified a special type of shock outflow process appearing to have relevance to other shock interactions, and notably to shock reflection from an oblique wall. For certain incident shock strengths and angles of incidence α, the air/methane refraction problem simulates closely the situation in the trouble-some range of the reflection problem, in which α lies between the value αe at which the theoretical solutions terminate and the value α0 that marks the onset of Mach reflection, and in which the flow deflections cannot be reconciled with theoretically permissible reflected shock strengths. In the analogous refraction cases, the reflected shock is observed to increase in strength along its length to a maximum value at the intersection point, and to be followed by a subsonic rarefaction zone which also increases in severity near the intersection. In fact, this zone appers to coalesce into a subsonic discontinuity, just at the intersection point—a feature which would contradict one of the basic assumptions of the regular reflection and refraction theories. Other refraction experiments suggest that a similar process is relevant to the Mach reflection configuration, and may account for the discrepancies in the three-shock theory for weak incident shocks.

On the multiperforate plates occurring in the xylem vessels of some monocotyledonous roots

The occurrence and structure of multiperforate plates in the xylem vessels of the roots of some monocotyledons are described. Such plates are present in all the vessel segments of the roots of many members of the family Araceae and inCrinum asiaticum. In all these plants vessel segments with simple perforations have not been observed. The vessel segments as found in these roots may be of three types : (i) those having oblique end walls at both ends; (ii) those having oblique end wall at one end and transverse or slightly inclined end wall at the other; (iii) those having transverse or slightly inclined end wall at both ends. The perforation plates of these segments may be scalariform, scalariform with branched bars, or reticulate. The bars of the plates can be correlated to the scalariform-reticulate thickening of the lateral walls of the vessel segments. These types of vessel segments are regarded as forming a primitive feature. Further it is concluded that the xylem vessels of roots have developed phylogenetically from typical scalariform tracheids by the loss of pit membranes at their ends.