REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



which the term " germ" may be applied in the 

 sense of the definition given at the outset, may 

 be included in one of two classes. The first 

 comprises zoospores and zoosporoid bodies ; 

 the second, all those forms of germ which re- 

 quire for their development a previous combi- 

 nation of two parts or organs, complementary 

 to each other as regards their reproductive 

 functions. 



27. Zoospores. Of zoospores we recognise 

 two kinds, simple and aggregate. The simple 

 zoospore is a pear-shaped or ovoidal body : it 

 is composed of transparent, colourless homo- 

 geneous plasma, throughout the whole of 

 which, with the exception of the smaller end 

 (rostrum), granules of colouring matter are 

 scattered. It possesses no investing mem- 

 brane, but is provided with a pair of cilia, the 

 directions and positions of which differ accord- 

 ing to the class. Every zoospore possesses 

 a single granule of a red or reddish-brown 

 colour, which is always placed in the immediate 

 neighbourhood of the colourless rostrum. Its 

 characteristic motion is a constant progression 

 in the direction of its axis, around which the 

 whole zoospore at the same time revolves, the 

 transparent rostrum being always directed 

 forwards. As regards the chemical composition 

 of the zoospore, the transparent and colourless 

 plasma is a nitrogenous compound, coloured 

 brown by iodine. The cilia, as far as their 

 reactions can be ascertained, resemble the 

 plasma from which they emanate. As to the 

 constitution of the coloured granules which 

 are scattered throughout the plasma, we have 

 as yet no direct observations ; but from the 

 form which they exhibit being that which is 

 always assumed by starch, not only among 

 the Alga?, but also in the green Infusoria, there 

 can be little doubt that they are composed of 

 that principle, in mechanical combination with 

 colouring matter and a fat. 



28. In passing from the condition of motion 

 to that of repose, or, in other words, in germi- 

 nating, the zoospore is not subject to any sus- 

 pension of its vegetative activity. From the 

 moment that it is set free from the parent 

 plant to that at which it begins to develope 

 from itself a new plant similar to the parent, 

 it continues to grow uninterruptedly. 



29. Of the aggregate zoospore, the best- 

 marked example is that which has been fully 

 described in Vaucheria. In comparing the 

 termination of a fructiferous filament of Vau- 

 cheria, with the sporangium of Saprolegnia, 

 we can at once satisfy ourselves that these are 

 corresponding structures ; the distinctive dif- 

 ference being, that in the one the whole pro- 

 toplasma contained in the termination of the 

 tube is collected together to form a single large 

 zoospore, while, in theother, it is subdivided so 

 as to form a multitude of small ones. In other 

 words, the single zoospore of Vaucheria takes 

 the place of the collection of zoospores con- 

 tained in one sporangium of Saprolegnia. This 

 fact is all that we mean to imply by the use of 

 the term aggregate. 



30. Zoosporoid bodies. Among these we in- 

 clude the antherozoidsol'Cutleria, of the Fu- 



223 



caceae, of the Florideae, and of the Characeae. 

 Of the relations of the first two to the true zo- 

 ospore in form and development, we have al- 

 ready said enough in the preceding pages. Those 

 of the antherozoid of Charaare not so close; 

 and the structure of the organs in which they 

 are developed, differs so essentially from any 

 structure met with in any other family, that it is 

 inexpedient to found any notions of their nature 

 or formal relations upon sucfi slender analogies 

 as may exist. In the case of the Florideae, the 

 correspondence between the antherozoids and 

 the zoospores of other Algas, is still less trace- 

 able ; but the peculiar arrangement of the 

 bodies in question their being always deve- 

 loped in different individuals, though in similar 

 positions as regards the organs of vegetation 

 leads us irresistibly to the conclusion that 

 they have a mutual relation, or are in some 

 degree complementary to each other in function; 

 and as we know the production of germs to be 

 the function of the one, it is reasonable to 

 assign their fecundation to the other. 



Germs, whose development is dependent on 

 the combination of two organs the reproductive 

 functions of which are complementary each to 

 each. Of these it is the leading characteristic 

 that they do not necessarily pass at once, as 

 soon as they are set free from the parent, into 

 active development. If the necessary condi- 

 tions of temperature and moisture are absent, 

 they are capable of remaining in a state of re- 

 pose, without losing their power of germina- 

 ting. This state may last for weeks, or even 

 for months. Their second characteristic is 

 connected with the first ; viz. that they are 

 always provided with a distinct investing mem- 

 brane, on the strength of which their power of 

 resistance to external agents may in part de- 

 pend. This is well seen in the spores of the 

 Desmideag and Zygnemaceae. 



31. There remain a few examples of germ- 

 like bodies of uncertain signification, which are 

 included in neither of the above divisions. 

 Such are the various forms which occur among 

 the Florideae, the stationary spores of Sapro- 

 legnia, and others, of which, as they are still 

 imperfectly known, sufficient has been said in 

 the preceding pages. 



32. FUNGI AND LICHENS. While, on the one 

 hand, the Fungi and Lichens present an endless 

 variety in the organs which constitute their 

 reproductive system (receptacle), their vege- 

 tative system (mycelium, s/roma, Jlocci, hypo- 

 tfial/us, $c.), on the other, preserves a remark- 

 able degree of uniformity. It always consists 

 of a network of cylindrical hollow filaments, 

 usually divided at irregular intervals, but some- 

 times simple. In the latter case the whole 

 network, however complicated it may appear 

 at first sight, is in fact only a ramified cell. 

 This structure, which, in its simplest form is 

 the immediate result of the germination of the 

 spore, is the most permanent portion of the 

 plant, inasmuch as, although every part of it, 

 considered separately, is transitory, the vege- 

 tation of the whole is continuous, and its 

 duration unlimited. It is from it that the 

 organs which constitute the reproductive sys- 



