Ontogeny of the uredium of Melampsora lini

Light microscopy and transmission and scanning electron microscopy were used to study the development of uredia of Melampsora lini. Uredia were produced 6–10 days after inoculation with urediospores of M. lini. Uredium ontogeny began with the formation of a uredium initial from a hyphal plexus in a substomatal cavity. The hyphae oriented vertically and expanded; the enlarged ends divided to form a palisade of uredial initial cells. These cells divided into basal and terminal cells. Each terminal cell divided transversely to form a peridial and an intercalary cell; the basal cell became the sporogenous cell. The intercalary cells disintegrated early in the expansion of the uredium and released their contents into the intercellular matrix. The sporogenous cell, usually swollen at one end, gave rise by budding to successive sympodially produced spore buds which elongated and divided transversely to form pedicels and immature spore cells. As the spores matured the pedicels shriveled and became separated from the urediospores. Elongated, often capitate, paraphyses formed throughout the uredium and functioned to rupture the peridium and epidermis which covered the immature uredium. The peridium and the intercalary cells formed only once during ontogeny of the uredium, this being associated with only the first generation of urediospores. The intercalary cells were disrupted during uredium ontogeny, and most of the peridial cell layer was sloughed off, along with the overlying epidermis, upon rupture of the latter. The paraphyses were permanent and remained in the uredium throughout its functional life. Successive generations of urediospores arose within the same uredium from spore buds produced sympodially from the original sporogenous cell but without forming additional peridial or intercalary cells.

Studies on aecial development in rust fungi: Puccinia polliniae

The leaves of Goldfussia dalhousiana become infected by Puccinia polliniae with the onset of rains in the Western Himalayas. Pale yellow dots appear on the leaves, developing into pustules and extending centrifugally. Pycnia develop on the upper surface and aecia on the lower. Protoaecia are differentiated into fertile and displacement zones. After dikaryotization, the basal cells elongate, become binucleate, and, by transverse conjugate division, produce the aeciospore mother cells. By transverse division, each of these form a large aeciospore and a small disjunctor cell towards the basal cell. The basal cells at the periphery, by transverse conjugate divisions, give peridial mother cells each of which by an oblique conjugate division cuts off an intercalary cell towards the outside and a peridial cell towards the inside. The peridial cells develop thick walls and the intercalary cells degenerate. The peridium has a dual origin and the aecia are of the aecidioid type. The aeciospores are circular to oval in shape, binucleate, and multiguttulate. They have radially striate thickened walls and two to three germ pores.

Initiation and development of leaves in Douglas fir

The initiation and development of the leaves of Douglas fir is described in detail. Leaf initiation is similar to that of other foliar organs and involves both protodermal and peripheral cells of the apex. Apical and subapical initials are present but active for only a short time. Most enlargement is a result of intercalary cell division and enlargement. A limited marginal meristem is present. No differentiation of tissues occurs before bud dormancy in the fall. Growth following dormancy shows the various tissues to mature at different rates and all tissues are fully mature when the leaf becomes dormant in the fall. Growth periodicity of the shoot apex and the length of the growing season are discussed. Initiation and development of leaves in relation to all other foliar organs in Douglas fir are compared.

The Structure and Development of the Larval Cuticle of Diataraxia oleracea (Lepidoptera)

The main layers comprising the soft cuticle of the Diataraxia larva have been denned and a study made of their formation during development of the 5th instar larval cuticle. In soft cuticle the epicuticle is thrown into minute tubercles and consists of three layers--the cuticulin layer, the wax layer, and the cement layer. The cement layer lies outside or partly embedded in the wax layer, but it is either absent or extremely thin over the tips of the tubercles. A polyphenol layer is absent and it is suggested that this layer is present only in hard cuticle. Beneath the epicuticle is a thin, lightly tanned exocuticle approximately 0.5µ thick. The 7-10µ thick outer endocuticle is perforated by well-defined pore canals and consistsof lamellae containing chitin fibres varying from 100 to 2,000 Å in diameter. Pore canals are absent in the inner endocuticle which when fully developed may be more than 50µ in thickness. At 25°C, moulting of the 4th-5th instar takes less than 48 hours. The cuticulin layeris laid down about 12-24 hours before ecdysis. At about 6-12 hours before ecdysis the exocuticle is formed beneath the cuticulin layer in the outer part of the developing outerendocuticle. Formation of the wax layer begins about 1 hour before ecdysis, while the cement layer is secreted only a few minutes prior to ecdysis. The inner endocuticle is laid down during the 5 days after ecdysis. Prior to ecdysis the pore canals connect the hypodermis to the epicuticle and open into theexuvial cavity at the tips of the epicuticular tubercles. Probably the pore canal lumen is responsible for conduction of the moulting fluid. Each pore canal contains a well-defined strand of material which occupies but a small part of the pore canal lumen. Thfc pore canal strands, conduct protein and dihydroxyphenol from thehypodermis to form the exocuticle. Exocuticle formation is complete by about 1½ days after ecdysis. At this stage the pore canal strands become chitinized and sclerotized and the pore canals are cut off from the hypodermis by the developing inner endocuticle. The pore canalsare not responsible for transport of regenerative waxes from the hypodermis after abrasion of the epicuticle. In areas of hard cuticle there is a relatively thick and heavily tanned exocuticle which continues to develop during the life of the instar. The pore canals maintain contact with the hypodermis throughout the instar and probably remain functional as a conducting system for transport of exocuticular materials. A study of Verson's glands suggested that the large gland cell secretes a lipoprotein whichis discharged on the surface of the epicuticle to form the cement layer. The intercalary cell secretes a phenol which is responsible for the tanning of a plug that blocks the opening of the gland duct after discharge.