S81 



REPRODUCTION IN PLANTS AND ANIMALS. 



REPRODUCTION IN PLANTS AND ANIMALS. 



562 



aud structure of their receptacles, differ from them completely iu 

 the mode of origin of the spores. The simultaneous occurrence of 

 some of these forms, along with their ascophorous analogues, or, in 

 other instances, the successive development of both kinds of recepta- 

 cles in the same position, had been frequently observed, aud had 

 given rise in the minds of some mycologists to the suspicion of the 

 existence of a relation more close than was generally admitted. This 

 suspicion did not, however, take a sufficiently distinct form to lead 

 to observation, until the MM. Tulasne, iu a series of researches 

 scarcely completed, showed that the genera in question, hitherto con- 

 sidered as distinct, were in fact identical, and that receptacles con- 

 taining thecao and paraphyses, are produced on the same stroma, or, 

 in other words, on the same individual plant, as those which contain 

 acrogenous spores. 



"The earliest researches of MM. Tulasne were directed to the 

 Pyrenomycetes. In some species of Sphcuria, they found not only 

 that the same stroma produces receptacles with acrogenous spores, 

 which are followed by others bearing thecse, but that, under certain 

 circumstances, it may give rise to spore-bearing organs of a much 

 simpler character; namely, branching filamentous pedicles, bearing 

 at their terminations single spores, and rising directly from the 

 mycelium filaments, with which they are continuous. In this con- 

 dition the plant cannot be distinguished from a thread fungus, and 

 baa been hitherto described as such. 



"The later observations of MM. Tulasne, which are much more in 

 detail, refer almost entirely to Discomyeete.*, In a species of Rhytiima, 

 a genus of Discomycetcs, which inhabits the epidermis of the leaves of 

 plants, the stroma at first presents the appearance of a black spot of 

 various extent UL the surface of the leaf. In the substance of this 

 stroma the first receptacles are formed; they are cushion-shaped 

 capsules, furnished with apical apertures, like those of Sphceria, and 

 are entirely occupied by a pulpy nucleus, which consists of slender 

 branched filaments, often so long as to project considerably beyond 

 the aperture. These filaments bear at their extremities innumerable 

 minute linear sporules, which are enveloped in an abundant mucilage, 

 and are expelled from the ripe capsules in the form of a long cirrhus. 

 After the capsules, which are developed during the early summer 

 months, have discharged their contents, they are succeeded by the 

 lirelliform discs of the perfect Rltytitma. These do not arrive at 

 maturity until the following spring, and bear upon their upper surface 

 thectc and parapbyse*, like those of a Peziza. In other genera MM. 

 Tulasne found that the ascophorous receptacles are preceded by 

 capsule.*, which produce, instead of the linear sporules above men- 

 tioned, cylindrical spores of a much larger size, each of which is 

 supported at the extremity of a pedicle of its own. 



" Thug in the plants under consideration we find that, without 

 counting the sporules which are produced by filaments rising directly 

 from the stroma, there are no less than three varieties of spore-like 

 structures, which can be easily distinguished from each other. All of 

 these may be produced upon the same individual, and one is recorded 

 in which a capsule of a Peziza, was found, which bore, among the 

 normal thecse, paraphyses with innumerable slender linear sporules 

 at their extremities. As has been already hinted, the capsules which 

 contain aorogenous spores, have been hitherto considered as belonging 

 to genera distinct from those represented by the ascophorous recepta- 

 cles with which they were found associated. The genus C'ytiipora is 

 characterised by a structure which corresponds completely with that 

 of the capsules described above in Rhytisma ; and other genera, as, 

 for example, Sporocadut, have a similar relation to the capsules, 

 containing the larger variety of pedunculated cylindrical spores." 



We know less of the reproductive organs of the Lichens ; they 

 however closely resemble those of the Fungi- The following is a 

 summary of the reproductive organs found in these two orders : 

 1, Sporules which are formed by the constriction and separation of 

 the extremity of a simple cylindrical filament. 2, Spermatia, with 

 their supporting pedicels. 3, Stylopores, with their styles. 4, Thecfc, 

 or aci. 5, Basidia, with their basidia-spores. Although the evidence 

 u as yet imperfect, there is still good reason for supposing that the 

 asci and spermatia are truly sperm-cells aud germ-cells, whilst the 

 other organs represent the germs or buds. 



An account of the reproductive organs of the higher C'ryptogamia 

 will be found under the articles FIUCBS and Musci. That the organs 

 there described may be regarded as containing the two elementary 

 cells, which we have called germ-cells and sperm-cells, is now matter 

 of little speculation. Mr. Henfrey in a report mode to the British 

 Association in 1851, says, in regard to the question of sexes, "We 

 have several kinds of evidence : 



"1. The inferences to be deduced from the universality of the 

 existence of two kinds of organs in connection with the reproductive 

 process. We have seen that these exist in all the families at some 

 period or other of the life of the representative of the species. In 

 the Mosses and the Hepaticin they occur in the fully developed plant. 

 In the Ferns and Equisetawf they occur upon cellular structures of 

 frondose character developed from all the spores, which frondosr 

 1 or pro-embryos have an existence of some permanence, esp 

 cially in the Kqttitelacece. In the Lyeopodiacea, the ItoHtacea, and 

 ft/ii:ocarpe<r, the pistillidia occur upon very transitory cellular 

 itructiiren produced from one kind of spore, the larger, while the 



AT. HIST. DIV. VOI. IV. 



smaller spores at once develop in their interior cellules containing 

 moving spiral filaments such as occur in the antheridia of the other 

 families. 



"2. The inferences to be deduced from the observations on the 

 development of those plants in which the two kinds of organs, occcur- 

 ring in distinct places, can be separated. Strong evidence has been 

 brought forward that the dioecious Mosses, as they are called, do not 

 produce sporangia when the pistillidia are kept apart from the anther- 

 idia by natural accident. The majority of observers state that the 

 large spores of the Rhizocarpeai do not germinate if the small spores 

 are all removed from contact with them ; a few counter-statements 

 however do exist. Again, the majority of authors, and all the recent 

 ones, state that only the large spores of tho Lycopodiacete and hoe- 

 taceai produce new plants ; while some older writers believed that they 

 had seen the small spores do so. 



" 3. The direct observation of a process of fertilisation, of which we 

 have only testimony from two authors, Suminski and Mercklin, in 

 reference to the Ferns alone; since the assertions of Schleiden in 

 regard to the Rhizocai-pece have been demonstrated by Nageli, 

 Hofmeister, and Mettenius to have been based on very imperfect 

 observation." 



To the question as to the homologues of the organs in the higher 

 Cryptogamia, Professor Henfrey gives the following answer : 



" In the Mosses and ffepatiae the pistillidia occur upon the plant 

 when the vegetative structure is perfect, and the immediate product 

 of the great cell is a sporangium. If a process of fertilisation take 

 place here, we may regard the antheridia and pistillidia as analogues 

 of the anthers and pistils of flowering plants, the sporangia of their 

 fruits; or with Hofmeister we may regard the phenomenon as an 

 instance of an 'alternation of generations,' where the pistillidium 

 would be looked upon as an ovule, producing (in the sporangium) a 

 new individual of totally different character from that developed 

 from the spore (the leafy Moss plant in the usual acceptation of the 

 term). 



"In the Ferns and Equiselacece, we find the spores producing a 

 frondose structure of definite form, upon which are developed anthe- 

 ridia and pistillidia, or 'ovules.' Heie then we seem to have one 

 generation complete, and the new development from the pistillidium 

 or ' ovule ' appears in a totally new form, producing stem and leaves 

 which have a distinct individual form and existence, and produce the 

 spores after a long period upon temporary parts of the structure, on 

 the leaves ; and by no means cease to exist when those are matured. 

 Here we seem to have a real ' alternation of generations ; ' and Bof- 



meister compares the whole permanent plant of the Fern, or Et/uit 

 to the sporangium of the Mosses and Jlepalica. In all the other 

 families, the Lycopodiacece, Iioetacett, the Rhizocarpece, the pro-embryo 

 is a very transitory production, and is developed from a different 

 spore from the spiral filaments. This pro-embryo is clearly analogous 

 to that of the Ferns and Equiietaceai ; and if the existence of sexes 

 be a fact, we have here a dioecious condition as contrasted with a 

 monoecious condition in the two last named families. Hofmeister 

 here again assumes that the pro-embryo developed from the large 

 spore is an intermediate generation between the two perfect forms of 

 the plant. 



" It is rather difficult to decide upon the real analogies of these 

 structures with those of the flowering plants. The resemblance of 

 structure is so close between the pistillidia of the Mosses and 

 Hepaticce, and the 'ovules' of the other Vascular Cryptogams, that 

 they must be regarded as analogues, and then the former could not 

 well be conceived to be analogous to the pistils of flowering plants, 

 but rather to ovules ; if this be the case, the sporangium must be 

 considered the analogue of the perfect plant in the Fern, &c., and the 

 leafy stem as the analogue of the pro-embryo of the Ferns, &c. The 

 pistillidium of the Mosses can indeed hardly be regarded as analogous 

 to the fruit of a flowering plant, as in that case tho spores would be 

 ovules produced long after fertilisation ; and on the other hand, if we 

 consider the pistillidia of the Moss as an ovule, which it might be, 

 analogous to that of the Coniferas in which a large number of 

 embryonal vesicles or rudiments of embryos are produced after 

 fertilisation on the branched extremities of the suspensors then we 

 seem to lose the analogy between the product of the pistillidium of 

 the Moss and that of the ovule of the Fern, unless we would regard 

 the entire plant of a perfect Fern as analogous to the ovule of a 

 Conifer." 



We close this part of our subject with a tabular view (given in the 

 next page), of the analogies in the development of different classes of 

 plants, drawn up by Dr. Sanderson. 



The process of generation is much more clearly apprehended in the 

 flowering plants. Here we have two sets of organs whose functions 

 are clearly and definitely the preparation of germ-cells and sperm- 

 cells. The organ in which the germ-cells are prepared is called the 

 Pistil [PISTIL], whilst the Stamen [STAMBH], in that part of its struc- 

 ture called the Anther, elaborates the sperm-cells. In the pistil the 

 germ-cells are called Ovules, or Seed-Buds; whilst iu the anther the 

 sperm-cells are called Pollen, or Pollen-Grains. In the growth and 

 development of both these sets of organs great differences are observed 

 but their function is always the same. 



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