September, igo6.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



529 



definite function, i.e., as water-carriers from the root 

 upwards. Of the cells that remain living units 

 throughout their whole existence, some are set off as 

 assimilators of carbon from the atmosphere, others 

 as the further elaborators of this carbon into substances, 

 such as sugar and starch, that can be later made use of 

 by the cells. The cells set aside for reproductive pur- 

 poses arise in parts of plants specially constructed for 

 this, and the origin of these cells is to a large extent 

 governed by hereditary influences, and partly by cer- 

 tain peculiarities in nutrition. Their further behaviour 

 is also upon definite lines, and the formation of the egg- 

 cell, the influence of fertilisation, and the whole of the 

 phenomena concerned in the production of the embryo 

 point strongly to the influence of heredity. 



The dependence of any one part of a plant upon any 

 other is easily seen in the fact that the leaves and other 

 green portions of a plant are the only organs in the 

 higher plants (speaking generally) whereby carbon is 

 assimilated, and without the leaves the plant would 

 certainly die. Likewise the dependence upon the roots 

 for the greater part of the water taken in is another 

 instance of the same principle. 



The cells of the leaf manufacture from raw-materials 

 supplied from below, together with carbon obtained 

 from the carbon dioxide of the atmosphere, the sub- 

 stances needful for the nutrition of the protoplasm in 

 other parts of the plant; the leaves are dependent for 

 their water and salts upon the roots, which take in 

 these from the soil outside, and upon the wood, by the 

 mechanical action of which, aided by root -pressure and 

 the transpiration current,* the water and salts are con- 

 ducted. By taking instances such as these, it may 

 easily be shown that the various cells of a plant are 

 more or less dependent upon one another, and work 

 towards the same end, namely, the adequate growth 

 and extension of the whole organism, until such time 

 when the reproductive organs have developed and made 

 good the certainty of extension of the species. 



Moreover, the instances of transmission of stimuli 

 which we have already studied show us that a very 

 delicate and rapid means of res])onse exists in some 

 cases, which in the .Sundew and others is of the highest 

 importance to nutrition, and the reaction of certain 

 parts of plants to injury, by the formation of cushions 

 of callus, whereby injurious evaporation is prevented, is 

 a well-known example of the working of special cells 

 for the benefit of the whole community. 



Thus, by an examination of the individual cell, and 

 by the employment of certain biological reasons which 

 are found to hold good and tally with results obtained 

 by experiment, it is possible io gain a little insight 

 into the manner in which the cell works; we see that 

 protoplasm is the working substance, that external 

 stimuli pioduce measurable effects, and that growth 

 as a whole depends upon the results of these stimuli. 



There are undoubtedly many undiscovered factors at 

 work tending to produce the final result, and some of 

 these, it is to be hoped, will be elucidated by future 

 investigations. At the same time it must be remem- 

 bered that here we have only attempted to give an 

 outline of the value of the cell to the organism; but 

 that such an outline is indispensable if wc wish to enter 

 into further investigations. 



* The transpiration current is brouKht about cliiefly by the 

 evaporation of water from tlie leaves ; this starts a sort of osmotic 

 action, vva'er being drawn up from lower cells of progressively 

 decreasing concentration. 



The Study of Heredity. 



.Although some of the phenomena of heredity hav>; 

 been familiar to us for so long, our acquaintance v^ith 

 them has really been of a very superficial kind. It has 

 been recognised that in general the offspring' tend to 

 resemble their parents, and by observation of large 

 masses of individuals we have even been able to arrive 

 at a measure of the strength of this tendency; but of 

 the inheritance of some character in individual cases 

 almost nothing has been known. It is only within the 

 last few years that the attempt to formulate "laws," 

 such as will give a concise description of the observed 

 phenomena, has met with any success. 



The object of this article is to give an account of the 

 principal methods by which the work has been carried 

 on, and briefly to indicate some of the principles upon 

 which the study of heredity is based, without attempt- 

 ing to enter at all fullv into the details which must be 

 sought in more technical papers. There exist at the 

 present time two schools, which attack the problem 

 from very different standpoints and by verv different 

 methods of investigation. 



The Statistical MeJhod. 



The foundation for the work of the present school of 

 Biometricians was laid by Francis Galton when he ap- 

 plied the methods of statistics to the treatment of the 

 phenomena of heredity and variation. 



A series of observations is made upon some one 

 character throughout a very large number of individuals 

 of some race. The character chosen is susceptible 

 cither of quantitative tneasurement or of reference to 

 some group in a qualitative scale. The stature and 

 the eye-colour of man may be cited as instances of two 

 characters which were studied, among others, by 

 Galton. 



The measurements are carried out upon a large num- 

 ber of individuals taken at random from among the 

 general population. The results are arranged in a 

 table showing the number of individuals which come 

 under each degree of our scale, and may be represented 

 graphically by plotting on squared paper the vertical 

 ordinates representing the number of individuals who 

 possess the character in the degree indicated by the 

 corresponding abscissa;. 



The larger the number of measurements the nearer 

 the tops of the ordinates arc found to approximate to a 

 smooth curve. The character which is borne bv the 

 largest number of individuals, that is, which corre- 

 sponds with the highest point of the curve, is known 

 as the mtKle: and the curve will be one of three general 

 types according to the position which the mode occu- 

 pies. The mode may be median, the curve being 

 symmetrical about the mean character; it mav he 

 nearer either end of the curve, representing graphically 

 the fact that divergence from the mode in one direction 

 is more common than in the other: or. finallv. the curve 

 may show more than one peak, the intermediate values 

 occurring less frcqucntlv. This curve represents a 

 population which may be divided into two or more 

 groups, each with its own mo<lc. Intermedi.ite forms 

 are rare, so that there is generally no dlfliculty in 

 placing anv individual in its proper group. Variation 

 of this tvpe is known as " discontinuous," as opposed 

 to the continuous variation represented by curves of 

 the first two tvpes. 



The range of variation of the character throughout 



