REPRODUCTION IN PLANTS AND ANIMALS. 



REPRODUCTION IN PLANTS AND ANIMALS. 



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fora* of fsisji. Alga, and Infusorial Animalcules, which had received 

 difftrent generic names, are now found to belong to the same specie*. 

 The** variation* are found to be chiefly produced by the influence of 

 the third art of circumstances. The highent animal* and plant* are 

 however liable to great modifications of the activity of the formative 

 force by the operation of both physical and chemical circumstances. 

 Many insects are not hatched till a certain amount of external tem- 

 perature Ukei place. Plants will not produce their leave* without the 

 influence of light Tadpoles are not developed iuto frogs and toads 

 whan deprived of light and heat The ordinary bee is converted into 

 a quean-bee by the peoiality of it* food. The Brauiea oleraeea of 

 the sea-shore is converted into red and white cabbagges, cauliflowers, 

 and broccoli by garden culture. All cultivated plants exhibit more 

 or lees modification of their growth under the influence of physical 

 and chemical circumstance*. The dog, the pig, the horse, the sheep, 

 and man himself present varieties which are manifestly dependent on 

 external circumstances, and not on any change in the character of tho 

 formative or species-making force. 



That there i* no change in the character of this force is seen in the 

 tendency which all the forms of a particular species have to recur to 



definite type, or to cease to exist This is seen especially in the 

 case of cultivated plants and domesticated animals, which are subject 

 to the greatest varieties of form, but which nevertheless retain 

 through all, the evidence of a specific formative force. Thus, closely 

 allied as are the specie* of apple and pear (the Pyrut main* and Pyna 

 vmlgarit of botanists), and subject as they are to so great variations 

 that above a thousand forms of apple have been produced in Great 

 Britain alone, then is not the slightest tendency in any of these cases 

 towards confusing the specific character of the apple-tree and the 

 pear-tree. So with our domesticated animals. The horse and ass 

 will even breed together, but the hybrid is not prolific, and there is 

 no tendency on the part of the one species to degrade or develop into 

 the other. All the facts that are known with regard to the nature of 

 the formative force lead to the conclusion that it is specific and 

 not general, and that it is regulated by the same laws throughout 

 all time. 



In what is called the alternation of generations (GENERATIONS, 

 ALTERS AIIOB OF], it might be supposed that an exception occurred 

 to the ordinary process of generation. It will be seen however that 

 in all the cases in which this phenomenon occurs, that it results from 

 modifications of the ordinary processes of reproduction, and the 

 unusual disposition of the sperm-cells and germ-cells. 



Having made these general remarks, we shall now proceed to speak 

 more particularly of the process of generation as it occurs in plants 

 and "'"'. restricting this term to the phenomena which take place 

 as the result of the union of two cells. That reproduction in plants 

 which occur* a* the result of the growth of the same tissues from 

 single cells, when it results in the production of a bud, is termed 

 Gemmation or Sprouting. This kind of reproduction also takes place 

 in the animal kingdom, and amongst many of tho lower animals the 

 power of reproducing new individuals by a process of budding is 

 seen. To this process of forming new beings as it were, from single 

 cells, Professor Braun of Berlin has applied the term ' Verjungung,' 

 which has been translated by Mr. Henfrey ' rejuvenescence,' 



Amongst plant* the lowest position must be assigned to the families 

 Dialomaetct and Detmidiea, and it is amongst these that the most clear 

 evidence ha* been obtained of the union of cells in order to the pro- 

 duction of the mospora* from which the new beings are developed. 

 [Desmoiu ; DIATOM ACE Ji.] The union of two cells i* also seen in a 

 Urge number of Con/erraeea, especially in the groups to which the 

 Zygmrmata belung. [ZlQMau.1 



Although amongst the Alga the production of spore* can be traced 

 in so large a number of case* to the union of two cells, their niultipli 



, ii r 



bodies 



the higher form* of plant*.' 



In the Pungi we meet with a variety of reproductive organs. As 

 the** have been investigated very recently, we give the following 

 extract from Dr. Sanderson's account of the vegetable ovum iu tho 

 Cyclopaedia of Anatomy and Physiology :' 



The simples* form of reproductive organs in the Fungi are those in 

 which the spores occur on a basis or basidium. This form of organ 

 i* best seen in Oeuter. The next form of reproductive organs in the 

 fungi i* in the form of a vesicle or bag, which is called a theca, or 

 ascua. " Of the**, the first which we shall mention belong to a group 

 of subterranean plant*, of which the Truffle Is the best known example. 

 The receptacle of the Truffle consist* of a fleshy man, throughout 

 which numerous sinuous cavities are interspersed. Each cavity i* 

 partly lined, partly filled with the thectc and the cells upon which they 

 are supported. This receptacle, like that of all other Punyi with 

 which we are acquainted, originates from a pre-existing mycelium. In 

 it* unripe condition it displays on section a number of sinuous empty 



The rlfht <tw of tke tana ' Individual ' In Natural HUtorr Is s difficulty. 

 U Uw t*tm Is rntrlrtcd aaljr to Uw direct produce of the (rrm-crll and >perm. 

 cell, them oil trees raoaf <t*d br lip* belonf to the name Individual. In order 

 U confiM Uw ten* ladlvidaal lo mch c>M, It baa been proponed among animal* 

 la iie Uw tera mold or ioooit to the Independent itructure* which rnu'.t 



more ordinarily take* place by mean* of loospores or zoosporoid 

 , which are perfectly homologous with the buds or sprouts of 



cavities, which either communicate with each other, or open at one or 

 more points of the external surface. As the Truffle advances towards, 

 maturity the cavities are obliterated by the formation of a whitish 

 tissue, so that on section, we observe the whole to consist of two sub- 

 stance* the one translucent, of firm consistence, and of a dark-brown 

 colour; the other white and opaque. The former, which corresponds 

 to the partitions which, in the young state of the Truffle, separated 

 the cavities, is continuous with tho external tissue which composes 

 the envelope or peridium, and constitutes the vena interim of Vitta- 

 ilini. The lamiute 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 lamina;. 

 These tubes, which are the terminations of the filament* of which the 

 lamina) are composed, are of two kinds. Some are of equal diameter 

 throughout, and divi. led at intervals by septa; others much shorter 

 are dilated at their extremities, and contain spores (thceoo). Each 

 theca is an obovate vesicle, and contains two, three, or more spores, 

 never more than eight Each spore is invested with a beautifully 

 reticulate or sometimes warty epispore, within which may bo dis- 

 tinguished a smooth inner membrane, immediately inclosing the 

 oleaginous contents. 



" The ascophorous Punyi are represented in their simplest form by 

 the Uredinea, a family which has been studied by numerous observers 

 on account of the destructive properties of the plants belonging to it 

 The mass which is formed by the growth of the reproductive organs 

 of Undo under the epidermis of the leaves of the plants upon which 

 it grows parasitically, may be aptly compared to a pustule, a grum- 

 ous-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 irregular wall, or lining of pyriform cells, tho smaller ends of 

 which rest upon a raticular 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, resembling those first men- 

 tioned 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 tabular pedicle ; while in the club-shaped upper extremity 

 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 expense of the 

 protoplasm.!, so as almost to fill the theca. In other genera, as in 

 Phraymidium, there are pedicled cells of a similar form, arid originat- 

 ing in a similar manner, which however, instead of one spore, develop 

 a number iu their interior; these spores are arranged iu linear series, 

 and are formed in the same manner. The protoplasma however never 

 disappears completely, but remains as a more or less consistent mem- 

 brane, glueing the ripe spore to the spore-case which encloses it. 

 Some of the Uredinea possess a cyst which reminds us of the peri- 

 thocium of the Sph&riacetc, to which they are evidently closely related. 

 The cyst is formed ((Ecidium) of a single layer of roundish cells. 



" From the Uredinea we pass by a natural transition to the Disco- 

 mycetes and Pyrenomycetes. These plants have beeu investigated with 

 much success by Messrs. Tulasue, who have shown that they possess 

 the closest relationship not only to the Lichens, but to the most simple 

 thread Punyi. 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 Pyreno- 

 mycetes are represented by Spharia, the receptacle of which consists, 

 as is well known, of a spherical cyst, which is open above. Its wall 

 is frequently prolonged upwards iuto a tubular beak, which projects 

 beyond the surface of the bark or wood in which the whole plant is 

 imbedded. The membrane of the cyst (perithecium) ia usually com- 

 posed of polygonal tabular cells ; it is lined by an inner layer, formed 

 of the commencement* of the paraphyses and thectc, and of the 

 filament* with which they are connected. The theoo are obovate 

 cells, the membrane of which is of i-xtreme delicacy. When fully 

 formed, they contain from three to eight oval spores, the epispores of 

 which are in the early condition delicate and pellucid, but by degrees 

 become brown and opaque. The contents of the spores, as is 

 observed throughout the higher Fungi, consist of a fluid loaded with 

 oily granules. The thecaj are arranged with their long axes perpen- 

 dicular to the inner surface of tho perithecium from which they 

 spring, and are intermixed with a greater or less number of slender 

 cylindrical paraphyses. The whole perithecium is usually enveloped 

 in the filamentous stroma or mycelium, from which it takes its origin. 

 The Discomyoetes are represented by the Patua: ; between these and 

 the Spkceria there are differences of external form, which, though 

 they strike the superficial observer aa important, are in reality trivial. 

 While the receptacle of the Spharia is a cyst with an apical aperture, 

 that of the Peziza ia a cup-shaped disc, the concave surface of which 

 looks upwards. This surface is lined with an ascophorous membrane, 

 which resembles in every respect that of a Sihceria. 



" Along with the Pauas and Sphceria, and those allied genera which 

 resemble them in producing their spores inclosed iu theccc, there are 

 other forms also included in the 1'yrenotnycetes and Diseomyci-tei", 

 which, while they resemble tho*" last named in the general outline 



