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The anatomical structure of the epicarp of the peach and some particularities in the mesocarp
Davor Miličić
; Hrvatska
Sažetak
Neither the anatomy of fruit has been fully studied, nor has been sufficiently examined the anatomical structure of some most common cultivated plants. The literature is very scarce, so that the author (at the beginning of this study) could refer only to older, general studies about the development and the structure of juicy fruits (G a r c i n, L a m p e), and to data of bromatologists (Howard, Kochs) and to works of A. Niethammer.
In this paper there has been described the anatomical structure of the epicarp of two peach-varieties (Prunus persica S. et Z. var. vulgaris Maxim, and Prunus persica var. nuciper- sica C. K. Schneider), anogeom tracheids from the mesocarp and gummosis in the vascular bundles. Under the term of epicarp is meant the outer skin-tissue of the epicarp, that is to say the epidermis together with the hypodermis.
The researches were carried out during 1947 on the varieties Elberta, Alexander early, Mazia, Tardiva, Nectarina red and Lord Palmerston.
Prunus persica var. vulgaris
In most of the varieties (Elberta, Tardiva, Mazia and others) the epidermis of the epicarp has a special shape. This particularity is manifested especially in a cushion-like convex epidermis between hairs and therefore the epidermis is of different height on various places. Within the epidermis tangential walls develop on many places. A further characteristic of these cells is their smallness. (Fig. 3). Most of these cells touch the hairs directly being so under the direct influence of the hairs (Fig. 1). Comparing this epidermis with the one of Alexander early, which has much less hairs on one unit of the surface, shorter hairs and a straight surface, the author considers that the essential characteristic in the structure of the former epidermis i. e. its cushin-like convex form between the hairs is due to the great number of haiTs on a unit of surface and length of the hairs.
There are also emphasized some more important points in the development of the epidermis. From the epidermis of the young ovary begin to go out trichoms a short time before the flowering of the peach and even before the beginning of the formation of stomata. The period of the differentiation of the trichoms is a long one and lasts in the variety Elberta till the first half of June, when the differentiated trichoms die finally.
At the same time are formed cuticular layers (2—4 /t thick) underneath the cuticle of the epidermal cells, one part of the longer trichoms fall off and the inserted bases of the fallen trichoms and of those ones which remained, get covered with a cutinised layer.
On the epicarp can be distinguished three kinds of trichoms: 1. trichoms with sharp tops and thickened membranes, 2. trichoms with rounded tops, 3. trichoms with pointed tops and thin membranes. The first kind of trichoms is the most common one (Fig. 3.). The second is differentiated at the end of the developing-period of trichoms, when only short trichoms are developed, and the all trichoms of this form are short (Fig. 3.). The third kind is quite rare (Fig. 4.). All these trichoms have lignified membranes. Trichoms usually develop from the epidermal cells which occupy the whole height of the epidermis. If inside of the epidermal cells tangential walls develop, trichoms can be developed from the outer daughter-cell (Fig. 3.).
On the ripe fruits of the variety Alexander early are 3-—6 stomata on a mm2, of which a part is out of function.
The hypodermis consists of 2—6 layers of parenchyma- cells with the thickened membranes. The tangential membranes, and those in the corners of the cells are more thickened than the radial ones.
Prunus pérsica var. nucipersica
At this variety are found among big epidermal cells also the small ones with very tiny lumen. This variety compensates the loss of hairs with better developed cuticular layers (cca thick). In the side-membranes are developed cuticular »ribs« and in the corners a little longer cuticular wedges. The subsidiary cells of the stomata are less cutinised and have less developed cuticular ribs, or these ribs are completely missing (Fig. 5, 6.).
The cutinising of the epidermal membranes is strong already in May at the variety Nectarina red. At that time die the guard cells of the stomata, but a part of stomata still remain open, so that the exchange of gases can be accomplished. On the ripe fruits of the variety Lord Palmerston are found 4—9 of such dead stomata on 1 mm2. On the ripe fruits are very often found cracks in the outer membrane of the epidermis.
The hypodermis is built in the same way as in the pilose variety, but the cells of this variety are bigger and the membranes thicker (Fig. 7.).
Anogeom-tracheids* and gummosis in the vascular bundles of the mesocarp
The vascular system passes through the parenchyma of the mesocarp toward the periphery of the fruit. Its branches near the epicarp forming a dense network. There are found many ends of the bundles in the form of anogeom-tracheids, in the depth of 0,2—0,7 mm underneath the outer epidermis of the pericarp (Fig. 8.). By their genesis, these anogeom-tracheids are evidently metamorphosed ends of bundles. The anogeom and other tracheids in the peripheric part of the fruit have spiral thickenings or thickenings with transversal pits. H o w a r d’s statement, that in the peach-fruit there are no vascular elements with spiral thickenings present (M o 11 e r-G r i e- b e 1) is not correct. Similarly to the tracheids of the fruit are built the anogeom-tracheids in the leaves of the peach. Within the bundles of the mesocarp there are hollows filled with gum (Fig. 9.). Gummosis in the bundles is a usual phenomenom of all the peach-fruits. This phenomenon has stated Beijerinck in the bundles of the fruit of Amygdalus communis and Amyg- dalus amygdalo-persica and proved that the formation of gum is not a pathological process, but a normal life-phenomenon. He considered that gummosis did not appear in the vascular system of the peach-fruit, but it is stated here that it appears also in the peach.
Ključne riječi
Hrčak ID:
152593
URI
Datum izdavanja:
31.12.1949.
Posjeta: 1.996 *