600 



SCIENCE 



[N. S. Vol. XLIX. No. 1278 



dration in their earlier stages, and later the 

 enlargement of the syneretic cavities in the 

 colloidal structure is followed by the distend- 

 ing or stretching action of osmostic pressures 

 in the vacuoles thus formed. 



8. Illustrations by records of growth of leafy 

 stems, joints of cacti, fruits of Solanum and 

 trunks of trees. 



The development of an organism from the 

 single- or few-celled stage to the stature of 

 the adult individual is generally characterized 

 as growth. One of the first facts that comes 

 to the notice of the observer who follows the 

 life history of an animal or plant from the 

 egg or the spore or from the resting stage in 

 a seed to maturity is that all parts of the 

 individual do not enlarge at the same rate, 

 and that if attention be fixed upon the most 

 readily available object for such a study, the 

 root or shoot of any plant, it will be seen that 

 the power of expansion seems to reside only 

 in the region of the tip in the case of the 

 root and in the tip and in certain regions 

 in the younger intemodes of stems, while such 

 organs as the leaves of grass elongate by the 

 action of a growing zone at the bases. There 

 are of course many specializations of this ac- 

 tion such as those displayed by simple organ- 

 isms in which a single cell is the inidvidual 

 and when this reaches full size all possible 

 growth is accomplished. As our principal pur- 

 pose in the present discussion is to present the 

 action of the protoplasm in growth it has 

 been found most convenient to use facts dis- 

 covered by the measurement and analyses of 

 plants consisting of many millions of cells. 



"With magnifications of much less than a 

 hundred, we readily see that the embryonic 

 cells of a plant which may be imagined as 

 of a cubical or prismatic form and consisting 

 of a dense mass of colloidal matter, become 

 larger, that they also change form, show new 

 structures in the mass and that the enclosing 

 wall takes on a variety of forms. These 

 changes determine the final part which the 

 maturing cell may play in the complex proc- 

 esses of the organism. The architecture of 

 the plant includes many beautiful mechanical 

 designs and it would be well to guard against 



the error of considering it as simply a set 

 of sacs, test tubes, and bits of jelly by recall- 

 ing the fact that it is, like all living things, 

 an engine which not only picks up its fuel, 

 manufactures it into briquettes, or their phys- 

 iological equivalent, bums this fuel, the de- 

 rived energy being used in a variety of ways, 

 but while this is going on the machine is also 

 adding to, repairing and altering its own 

 parts. This, however, does not imply that 

 any special or mysterious " life forces " are 

 concerned. The physiologist may in fact 

 identify a large number of the things that 

 may happen in the cell and he may imitate 

 many of them and the progress of science 

 will be marked by the successive subjugation 

 of others, but to assemble the material in a 

 way to obtain the complexity and the se- 

 quences of reactions of living matter is be- 

 yond our capacity for manipulation, and our 

 failure may not be ascribed to the lack of any 

 elusive vital spark. 



The taste for polysyllabic definitions of pro- 

 toplasm has waned and we are not so much 

 concerned with inclusive descriptions as with 

 an understanding of the nature of the sub- 

 stances which enter into its composition and 

 how these react when subjected to conditions 

 which may prevail in the cell. Protoplasm 

 when viewed with a low power microscope aj)- 

 pears to be a silvery translucent mass of mate- 

 rial like a highly hydrated jelly, which, in 

 fact it really is, being composed of about one 

 to two parts of solid matter to about two hun- 

 dred of water. The constituency of the solid 

 part, or the residue which is obtained by 

 driving off all of the water is a matter of no 

 little interest, since it is upon this physical 

 basis that all of the properties of the organism 

 rest. 



The proteins or albumins are invariably 

 present, and the transformations in the highly 

 complex molecules of the nitrogenous com- 

 pounds in living matter offer some tremen- 

 dous difficulties in interpretation and at the 

 same time yield the material for some of the 

 most romantic chapters in biological science. 

 Present in every cell, these substances may 

 not move from one protoplast to another ex- 



