REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



226 



sistence and of a dark-brown colour ; the other 

 white and opaque. The former, which cor- 



Fig. 145. 



Sectfon o/par< o/ fAe receptacle of a Truffle, about 

 250 



a, outer layer of the peridium consisting of a 

 resistant tissue of thick- walled cells ; b, inner layer 

 of the same, formed of filamentous tissue continu- 

 ous with that of v, one of the venae internae, or par- 

 titions by which the compartments (originally 

 cavities) of the truffle are bounded. Portions of 

 two of these compartments are seen with the thecae 

 and septate filaments which they contain. 



responds to the partitions which, in the young 

 state of the truffle, separated the cavities, is 

 continuous with the external tissue which 

 composes the envelope or peridium, and con- 

 stitutes the vena interne of Vittadini.* The 

 laminae which it forms, consist of filaments 

 running, for the most part, parallel to each 

 other. The white substance which occupies 

 the original cavities of the tuber, is formed 

 of closed tubes, which are given off in great 

 numbers from the surfaces of the laminae. 

 These tubes, which are the terminations of 

 the filaments of which the laminae are com- 

 posed, are of two kinds. Some are of equal 

 diameter throughout, and divided at intervals 

 by septa ; others, much shorter, are dilated at 

 their extremities, and contain spores (thecae). 

 Each theca is an obovate vesicle, and con* 

 tains two, three, or more spores, never more 

 than eight. Each spore is invested with a beau- 

 tifully reticulate, or sometimes warty epispore, 

 within which may be distinguished a smooth 

 inner membrane, immediately enclosing the 

 oleaginous contents.*}* 



* Vittadini, Monog. Tuberacearum, p. 2. et seq. 

 f L. R. & C. Tulasne, Histoire des Champignons 

 hypogees, 41-50. 



37. The ascophorous Fungi are represented 

 in their simplest form by the Uredineae, a 

 family which has been studied by numerous 

 observers on account of the destructive pro- 

 perties of the plants belonging to it. The 

 mass which is formed by the growth of the 

 reproductive organs of Uredo under the epi- 

 dermis of the leaves of the plants upon which 

 it grows parasitically, may be aptly compared 

 to a pustule, a grumous-looking substance, 

 occupying, as it were, the place of the pus. 

 On more minute examination of the cavity, 

 we find that it is bounded by a kind of irre- 

 gular wall or lining of pyriform cells, the 

 smaller ends of which rest upon a reticular 

 cushion of mycelium. These are probably the 

 enlarged extremities of the mycelium filaments, 

 with which many of them can be distinctly 

 traced to be connected. Towards the base of 

 the cavity other cells are developed, resem- 

 bling those first mentioned in their general 

 form, as well as in their relation to the myce- 

 lium. In these, however, the membrane is 

 produced inferiorly, so as to form a tubular 

 pedicle ; while in the club-shaped upper ex- 

 tremity it is lined by a considerable deposit of 

 granular protoplasma, so that here the central 

 cavity is very much smaller than that of the 

 external membrane. It is in this cavity that 

 the spore is formed, at first not exceeding it 

 in size, but afterwards increasing at the ex- 

 pense of the protoplasma, so as almost to fill 

 the theca. In other genera, as in Phragmidium, 

 there are pedicled cells of a similar form, and 

 originating in a similar manner, which, how- 

 ever, instead of one spore, develop a number 

 in their interior ; these spores are arranged in 

 linear series, and are formed in the same 

 manner. The protoplasma, however, never 

 disappears completely, but remains as a more 

 or less consistent membrane, glueing the ripe 

 spore to the spore-case which encloses it. 

 Some of the Uredineae possess a cyst which re- 

 minds us of the perithecium of the Sphoeriaceae, 

 to which they are evidently closely related. 

 The cyst is formed (QEcidium) of a single 

 layer of roundish cells.* 



38. From the Uredineas we pass by a natural 

 transition to the Discomycetes and Pyreno- 

 mycetes. These plants have been investi- 

 gated with much success by MM. Tulasne, 

 who have shown that they possess the 

 closest relationship not only to the Lichens, 

 but to the most simple thread Fungi. The 

 very remarkable facts which these observers 

 have discovered, render the study of these 

 plants more satisfactory and instructive than 

 that of any other family of the class. The 

 Pyrenomycetes are represented by Sphoeria, 

 the receptacle of which consists," as is well 

 known, of a spherical cyst, which is open 

 above. Its wall is frequently prolonged up- 

 wards into a tubular beak, which projects 

 beyond the surface of the bark or wood in 

 which the whole plant is embedded. The 

 membrane of the cyst (perithecium) is usually 



* }j. R. Tulasne, Recherches sur les Uredine'es, 

 &c. Ann. des Sc. Nat. 3me. S. t. vii. p. 12. 



