Ralph H. Wetmore

A Paraffin Method for Refractory Plant Materials

A modification of Zirkles n-butyl alcohol method for dehydrating refractory plant material and embedding it in paraffin is described. The material is cut into small pieces and killed and fixed in CRAF III. It is dehydrated in Zirkles n-butyl alcohol series, slightly modified. Infiltration is accomplished by adding chips of paraffin of low melting point (52°C.) to the bottle containing butyl alcohol and the tissues at a gradually increasing series of temperatures. The butyl-alcohol-paraffin mixture is gradually replaced by pure paraffin (melting point 56-58°C). The material is embedded in Fisher Tissuemat (56-58°C). Before microtoming, the block of embedded tissue is trimmed so that part of the specimen is exposed, and it is soaked in water until it cuts easily.

Organization and Significance of Lenticels in Dicotyledons. I. Lenticels in Relation to Aggregate and Compound Storage Rays in Woody Stems. Lenticels and Roots

1. Lenticels may with advantage be considered transverse or longitudinal, in accordance with the orientation of the fissure. 2. The orientation of the cauline lenticel is clearly correlated with the nature of storage ray within. 3. Forms with aggregate storage rays of primitive nature in the stem, that is, composed largely of congeries of uniseriate rays, possess transverse lenticels. In contrast, these species in which the storage aggregations consist of multiseriate units, for the most part, are found to have longitudinal lenticels. In the latter cases the pericycle usually shows a disruption under the lenticular organs. Alnus, Corylus, and Carpinus typify this condition. 4. Forms with compound storage rays in the stem at maturity, but in which the compounding is completed only after many years, possess the more primitive lenticels, the transverse type. Those species in which the storage ray becomes compound within a very short time, one to three years, are found to have confronting each ray one or many longitudinal lenticels. These may even be so closely approximated as to appear as a single greatly elongated structure. Quercus offers the only example found of this situation. 5. Roots, irrespective of internal conditions and taxonomic affinities of the species concerned, all show paired appendage lenticels, the primitive type found to be characteristic of young coniferous stems and all coniferous roots, indicating the conservative nature of the root. 6. The intimate relation between the type of storage ray and the form of lenticel facilitates a satisfactory aeration of the living tissues within the stele, with the consequent maximum metabolic activity.

Organization and Significance of Lenticels in Dicotyledons II. Lenticels in Relation to Diffuse Storage Rays of Woody Stems

1. Lenticels occurring on shrubs and trees possessing diffuse storage rays are directly related in position, structure, and size to those rays, just as they were in cases of forms with aggregate or compound rays. In this way the aeration of the rays and other living tissues is affected. 2. Transverse lenticels exist much less frequently on forms with diffuse storage rays than do longitudinal lenticels. When present, they are universally associated with vertically shorter storage rays. 3. Longitudinal lenticels are more characteristic of woody forms with diffuse storage rays. In these cases the rays are always longer vertically. Frequently they are very long or they are arranged in vertical rows. At such times the rays are confronted by greatly elongated lenticels or vertical rows of lenticels. 4. Some trees, as Tilia, Carya, Fraxinus, possess V-shaped rays in the phloem. These rays become greatly elongated as well. Such increases in width and length are brought about by meristematic activities in the phloem region of the ray. These broad rays are confronted by rows of lenticels, thus facilitating their aeration. 5. The general existence of a deep seated periderm in shrubs and of a rhytidome in trees makes possible a still more intimate connection between the lenticels and the rays within. 6. The organization and evolution of the storage rays in the stems of angiosperms has been accompanied by a parallel organization and evolution of the lenticels. In the root, however, the more primitive transverse lenticels in their original relationship to the appendages have been retained. This is in accord with the conservative nature of the root.