196 



KNOWLEDGE. 



[Septembee 1, 1899. 



for whilst some of the protoplasts assume the function of 

 only supporting their fellows, the others avail themselves 

 of the support, raise themselves from the level of their 

 original surface, and devote themselves to the function of 

 reproduction. And, moreover, certain aberrant and sessile 



Fig. 20. — Pseudo-plasmodium of PohispTiondylium violaceum, 

 (After Brefeld.) x about 25. 



forms of the Dictyostelium seem to show that this elevation 

 of a portion of the protoplasm is not necessary to repro- 

 duction, though it may well be that the greater exposure 

 to the ripening influences of the atmosphere and the sun 

 may render it beneficial to the organism, and so more 

 than compensate for the withdrawing from the function 

 of reproduction of a certain part of the protoplasm, and 

 applying it to the purposes of support alone. 



Unicelldlae Obg.'^nisms. — Leaving now the subject of 

 classification, and of the aberrant forms of myxies, we 

 return to the principal group. We have already dwelt 

 upon the fact that the myxies show all their vital powers 

 and all their capacity for development without the forma- 

 tion of a true cell- wall, or undergoing division by septa 

 formed in cells. It seems scarcely possible for organisms 

 living in the air to attain any considerable size or com- 

 plexity of form without the support of cell-walls, and 

 without the formation of vessels which assist the transfer 

 of noiuishment from one part to the other. 



But with plants inhabiting the water — a medium of nearly 

 the same specific gravity as the plant — and drawing their 

 nourishment directly from this medium, the case is different, 

 and the possibility of such organisms attaining con- 

 siderable proportions and complexity of outward form is 

 shown by a considerable group of Ah/a, for which there 

 has recently been formed a class called Multimicleatis, 

 which includes four orders with considerable differences 

 amongst themselves, but which all agree in possessing no 

 cell -walls, and, under ordinary conditions, no septum 

 dividing one part from the other. Each organism is thus 

 a single protoplast. These unicellular organisms, as they 

 are often called, show a capacity for developing a vast 

 diversity of forms, many of them very beautiful, and many 

 of them strangely mimetic of the forms of higher plants — 

 of the mosses, the lycopods, the conifers, the cactus tribe, 

 and the hymenomycetous fungi. Some of these organisms 



-i 



reproduce sexually, others asexually ; some attain very 

 considerable size — as in the genus Caulerpa, a beautiful 

 form of marine alga. " Nature," says Mr. Geo. Murray, 

 speaking of Caulerpa, " appears to have executed in the 

 form of this genus a tour de force in exhibiting the pos- 

 sibilities of the siphoneous thallus — in showing that it is 

 possible for a unicellular organism to display the varied 

 beauties of outward form characteristic of highly organised 

 types, to attain by means of a lattice-work of cross beams 

 within the cell body that mechanical support effected 

 by transverse septa and separate differentiated cellular 

 structures for other algse and for the higher plants." 



A consideration of these structures 

 impresses the mind very forcibly with . .^ 



the vast inherent capacities of proto- ~i 



plasm. Nature had two courses ' 



open to her, if we may so speak, as to , 



the mode of dealing with protoplasm 

 — endowed as it is with its varied 

 capacities — each of which she has 

 pursued to a certain extent. In the 

 one course of development the single 

 protoplast has remained a unit, and 

 has in this undivided condition per- 

 formed all the needful work of the 

 plant. In the other course, the pro- 

 toplasm has been broken up into 

 detached parts by the cell-walls, and 

 thus a division of labour has been 

 brought about or promoted which has 

 led to the highest results, and left the 

 unicellular organisms far in the rear. 

 The former course of development is 

 seen in the myxies, and, as we have 

 shown, reached a great development 

 both as regards size, form, and func- 

 tion, in such algffi as C'liderpu, The 

 other course of development is seen 

 of course in nearly all the other 

 members of the vegetable kingdom, 

 and reaches its highest results in such vast and complex 

 organisms as our forest trees. 



One other observation naturally arises from the con- 

 sideration of these unicellular forms. We are wont to 

 trace the origin of the differentiation of parts — ^of the 

 branches and leaves and so forth^to the divisions of the 

 cell of the growing points in plants. We now see a 

 differentiation of parts arising without any such cell to 

 divide, and without any septa to mark off the future organ. 

 The protoplasm is the master ; the cell-walls are its 

 humble servants, and we have another illustration of how 

 the contents are apt to rule the containing structure, and 

 the soft to rule and mould the hard. The divisions of the 

 cell-walls are a secondary and subordinate phenomenon. 



Isomorphism. — We crave our readers' leave to return to 

 the fact already mentioned, that unicellular organisms 

 have a tendency to imitate the forms of cellular organisms, 

 and that whereas we have in the series and chain of cellular 

 plants such marked outward forms as those of the moss, 

 the lycopod, the conifer, the cactus, ic, we have in the 

 chain of unicellular plants very similar outward forms, so 

 that we seem to have two chains branching off' from one 

 another, with links here and there which closely corre- 

 spond with one another. This phenomenon is one found 

 frequently to present itself to the attention of the philo- 

 sophical systematist, and like all the phenomena of 

 Nature is well worth pondering. It has been stated very 

 forcibly by Mr. Brady, in respect to the Foraminifera, 

 a group of organisms deeply studied by him : — " A 



Fia. 21. — Immature 

 Sporangium of Poll/- 

 fiphondyliiim violaceum. 

 (After Brefeld.) 



