514 



NA TURE 



[September 2S, 189; 



of growth, which he carried out with the help of the 

 various forms of auxanometer invented by him. His 

 results, which first established the extreme complexity of 

 the conditions on which the rate of growth in plants 

 depends, are familiar to readers of his text-book and 

 lectures. 



The seventh section contains the papers on "tropisms,'" 

 i.e. the reactions of growing organs under the stimuli of 

 gravitation, light, and moisture. The last paper in the 

 group, that on orthotropous and plagiotropous organs, 

 seems to us to be of the widest interest, as offering a con- 

 tribution towards the solution of the most fundamental 

 and most difficult of all biological problems, namely the 

 question of the causes of the forms of organisms. This in 

 the author's phrase is the problem of " scientific morph- 

 ology." 



Section VI II., on the relations between cell-formation 

 ana growth, includes the two well-known papers on the 

 arrangement of cells (1878-9) in which the form of the 

 network of cell- walls is explained with the help of the 

 law of their rectangular intersection. The author shows 

 how, in organs of similar outline, identical arrangements 

 of the cells arise, whatever may be the morphological 

 nature of the organ, so that the cellular structure of a 

 hair, an antheridium, and an embryo may be the same. 

 He has thus given a useful warning to morphologists, 

 who have often laid too much stress on mere cell-arrange- 

 ment in discussing embryological and other similar 

 questions. 



The last paper in this section is on " Energids and 

 Cells." As it is the most recent of all (1892), and probably 

 the only one in the book which may not yet be familiar 

 to botanical readers, a short account of its contents may 

 be useful. 



Under the term energid. Prof Sachs understands a 

 single nucleus, together with the protoplasm governed by 

 it, the two together forming a whole, which is an organic 

 unit, both in the morphological and physiological sense. 

 He has chosen the name energid in order to express the 

 chief property of the organic unit, namely, that it pos- 

 sesses internal or vital energy. The conception of an 

 energid, as distinct from that of a cell, has become ne- 

 cessary, owing to the discovery in recent years of so many 

 multinucleate cells and multinucleate organisms without 

 cellular structure, discoveries which we chiefly owe to 

 the researches of Schmitz. Such a multinucleate cell or 

 organism, though enclosed within the contour of a single 

 cell-wall, is manifestly equivalent not to a single uni- 

 nucleate cell, but to a multicellular structure. This is 

 proved by the fact that the portions of protoplasm, 

 each surrounding a nucleus, so often subsequently 

 become free as complete and independent cells, as in the 

 formation of the zoospores of Saprolegnia, or form a 

 multicellular tissue, as in the endosperm of many 

 Phanerogams. 



It is quite evident that the word cell has come to be 

 used in many different and inconsistent senses. As 

 Prof. Sachs says : " According to the prevailing termi- 

 nology, an empty wood fibre is a cell, so is an embryo- 

 sac containing young endosperm, and so also is an 

 Amoeba, or a zoospore, or even an entire Caulerpa." 

 Everyone who has had to teach botany will sympathise 

 with the author in his complaints of the confusion thus 

 NO. 1248, VOL. 48] 



caused. While other sciences keep their technical 1 

 guage up to date, " the science of living things beg 

 with a word which arose more than 200 years i 

 in consequence of a mistake." Hence, in his opinio: 

 radical change in language is demanded ; for the ti 

 histological unit the word energid is proposed, while I 

 old word cell can be retained, either for the cell-w 

 alone (its original sense), or for the cell-wall togetl 

 with its contents, whatever they may be, and whetl 

 including one energid or many. 



It appears to us that the change proposed is a real a 

 great improvement ; the only difficulty is our firmly fij 

 habit of connecting the idea of a histological unit w 

 the word cell. Whether the new term be adopted 

 not, Prof. Sachs has dons good service in bringi 

 clearly before us the contradictions between our presi 

 antiquated phraseology and histological facts as tl 

 are now known to us. 



The ninth and last section of the work is on 1 

 causal relations of the form of plants. It consi 

 mainly of the two essays on " Staff und For:nl' wh: 

 have already attracted much attention, and met w 

 much criticism. The fundamental conception on wh: 

 these essays are based, is the idea that the organs 

 plants owe their form to their substance, just as a crys 

 owes its form to the chemical constitution of its mo 

 cules. Prof. Sachs, therefore, believes that there m 

 be a special substance concerned in the formation of ea 

 kind of organ ; there must be a root-forming substan 

 a shoot-forming substance, a flower-forming si 

 stance, and so on. Of course the quantity 

 the active substance by which form is deti 

 mined may be extremely small in comparison with t 

 whole material of which the organ consists. Prof. Sac 

 supposes that these hypothetical formative substanc 

 are, in the case of green plants, produced in the assic 

 lating organs, and thence conveyed to the seats of deveic 

 mental activity. He is inclined to identify the format! 

 substance with the nucleinc, and is so far in agreeme 

 with many modern histologisls. He regards the dilTere 

 specific formative substances as being possibly varieti 

 of nucleine, comparable to the isomers of grape-sugar, 

 of tartaric acid. 



The extremely hypothetical character of the whc 

 theory is manifest. The re is at present no evidence f 

 the existence of specific formative {e.g. " root- forming 

 or " shoot-forming "j substances. Even if we acce] 

 nucleine as representing them, we still have no evidenc 

 that it is formed in the assimilating organs, or indee 

 that it exists, as such, anywhere except in the nuclei 

 itself. So far as we know at present it seems that tl 

 nucleus forms the nucleine, not the nucleine the nucleu 

 Until some basis of fact is found for the " Staff ui. 

 Form " hypothesis, it can only be regarded as a formJ 

 not a real explanation of the phenomena, howevi 

 valuable it may be as a stimulus to further enquiry. 



An addendum to the last paper gives an extract froi 

 the Lectures on the Physiology of Plants (ist editioi 

 1882), on the continuity of the embryonic substance. 1 

 certainly seems to us that Prof. Sachs' idea here e) 

 pressed is essentially the same as the conception of th 

 continuity of the germ-plasm, which has played so impor 

 tant a part in recent biology. The form in which th 



