388 



NA TURE 



[March 14, 1878 



surer. It too depends on the compression of air, but in it the 

 extent to which the air has been compressed is marked directly 

 on the interior of a straight glass tube by the chemical action 

 of sea-water on a preparation of chromate of silver with which 

 the tube is lined internally. Between the salt of the sea-water 

 and the chromate of silver a double decomposition takes place. 

 Tiie chlorine leaves the sodium of the common salt and com- 

 bines with the silver, while the chromic acid and oxygen leave 

 the silver and combine with the sodium. Thus chloride of silver, 

 white and insoluble, remains on the glass in place of the Orange- 

 coloured chromate of silver lining as far up as the water has been 

 forced into the tube, and the chromate of sodium dissolved in 

 the water is expelled as the air expands when the tube is brought 

 to the surface. 



My navigational sounding machine was brought into practical 

 use for the first time in the steamship Palm, belonging to 

 Messrs. Charles Horsfall and Co., Liverpool, in a voyage to 

 Odessa and back about a year ago, in command of Capt. E. 

 Leighton. I cannot illustrate the use of the machine better 

 than by reading to you an extract from a letter I received last 

 April from Capt Leighton, describing his experience of it in this 

 first trial : — 



"During the voyage in the Palm steamship, which has just 

 come to an end, I took frequent opportunities of testing the 

 sounding machine when I had a chance of cross-bearings to 

 verify the depths as shown by chart, and always found it most 

 accurate. For instance, going up through the Archipelago and 

 just after clearing the Zea Channel, I got a good position by 

 bearings, chart showing seventy-nine and seventy-six fathoms, 

 two casts of your glass gave seventy-eight and seventy-five 

 fathoms. In the Bosphorus also it gave capital results in thirty 

 to forty fathoms water. 



'• " The first real use I made of the machine was in the Black 

 Sea during a fog which obscured everything. Wishing to 

 make sure of my position I put the ship's head for the land 

 and kept the machine at work. After running in to thirty 

 fathoms at full speed I slowed down and went in to twelve 

 fathoms, then hauled out to a convenient depth and put her on 

 the course up the coast. When it became clear I found myself 

 in a proper position, and no time had been lost by stopping to 

 sound. 



" Plow many shipmasters let hours go by without obtaining 

 soundings either because of the delay or on account of the 

 danger of rounding- to in heavy weather to get them, when, if 

 they were provided with your sounding-machine, they could have 

 their minds set at ease by having timely warning of danger, or 

 by knowing that they were in a good position ! " 



I had myself very satisfactory experience of the usefalness of 

 the sounding machine in coming up Channel running before a 

 gale of south-west wind m thick weather, on the 6th and 7th of 

 last August, on returning from Madeira in my yacht — a small 

 sailing schooner of 126 tons. About 5 A.M. on the 6th I took 

 two casts and found ninety-eight fathoms (sand and red spots) 

 and lOi fathoms (sand and small shells). The mean with a 

 correction of 2 J fathoms to reduce to low water, according to the 

 state of the tide at Ushant at the time, was ninety-seven fathoms. 

 Thenceforward I took a sounding every hour but one till eight in 

 the evening. By writing these soundings on the edge of a piece of 

 paper at distances equal according to the scale ot the chart to 

 the distances run in the intervals, with the edge of the paper 

 always parallel to the course, according to the method of Sir 

 James Anderson and Capt. Moriarty, I had fixed accurately the 

 line along which the vessel had sailed, and the point of it which 

 had been reached, with only a verification by a noon lati- 

 tude. At 6 o'clock next morning, by the soundings and course, 

 with proper allowance for the flood-tide, I must have been about 

 thirteen miles magnetic south of the Start, but nothing of the 

 land was to be seen through the haze and rain ; and with the 

 assistance of about ten more casts of the lead (by which I was 

 saved from passing south of St. Catherine's) I made the Needles 

 Lighthouse right ahtad, at a distance of about three miles, at 

 2 P.M., having had just a glimpse of the high cliffs east of Port- 

 land, but no other sight of land since leaving Madeira and Porto 

 Santo. In the course of the 280 miles from the point where I 

 struck the lOO fathom line to the Needles, I took about thirty 

 casts in depths of ico fathoms to nineteen fathoms without once 

 rounding-to or reducing speed ; during some of the casts the 

 speed was ten knots, and the average rate of the last 220 miles 

 was a little over nine knots. 



It is a pleasure to me to be able to add that the sounding 

 machine has also been successfully used in the Royal Navy, 



Admiral Beauchamp Seymour and Capt. Lord Walter Kerr 

 having kindly taken it on board H.M.S. Mino'aur for trial last 

 summer. Lord Walter Kerr wrote, on his return from Vigo, 

 regarding it as follows : — 



" The sounding; machine is most serviceable. We have been 

 using it constantly when running up Channel, from the time of 

 crossing the line of soundings to the time of reaching Plymouth, 

 and though running before a gale of wind with a heavy sea, at 

 the rate of ten knots, we were able to get soundings as if the 

 ship had been at anchor. We were able to signal to the squadron 

 each sounding as it was obtained ; thus, in thick weather, 

 verifying our position by soundings without having to round the 

 ships to." 



THE ANALOGIES OF PLANT AND ANhMAL 

 LIFE ' 



T ET us begin our inquiry into the analogies of plant and 

 ^-^ animal life by comparing the egg of an animal with the seed 

 of a plant. Let it be the ripe seed of a common plant, and 

 the egg of a bird. Both seed and egg may be said to consist of 

 the young creature and a supply of food which is stored up for 

 its use, and is gradually exhausted as the young creature develops. 

 Every one who has tried when a boy to blow a late bird's egg 

 must have been painfully alive to the fact of its containing a 

 young animal, and the egg we eat for breakfast may serve to 

 remind us of the store of food which we diverted from its proper 

 course of nourishing a young chicken. 



Here is a diagram representing a section through the seed 

 of a poppy, in which the young plant may be seen lying 

 in its store of food containing a supply of carbohydrates 

 and nitrogenous matter, which is consumed as the yolk of 

 the egg is consumed by the young chicken. Other seeds, such 

 as a bean, an acorn, or an almond, seem at first sight to consist of 

 nothing but the young plant, and to have no store of food. The two 

 halves into which a pea split are the two first leaves or cotyledons 

 of the young plant, the embryo stem and root being represented 

 by the little projecting mass lying between the two halves at one 

 end of the seed. Here the store of food is laid up in the body 

 of the young plant just as many young animals carry with them 

 a store of food in the shape of the masses of fat with which they 

 are cushioned ; the two leaves which seem so gigantic compared 

 with the rest of the plant are filled with nutriment, and perform 

 the same function of supplying food for the growth of the seed- 

 ling, which is performed by the mass of nutrient material in 

 which the embryo of the poppy seed is embedded. Recent 

 researches have shown that embryo plants are possessed of 

 powers which even in the present day it seems almost ludicrous 

 to ascribe to them. I mean powers of digestion. Gorup- 

 Besanez,^ a distinguished German chemist, found that in the 

 germinating seed of a vetch a ferment exists similar to the ferment 

 in the pancreatic secretion of animals — a secretion having the 

 power of reducing both nitrogenous bodies and starch to a con- 

 dition in which they can be utilised and absorbed by the tissues, 

 so that the embryo plant behaves exactly as if it were a minute 

 animal digesting and absorbing the store of food with which it 

 is supplied. The power of digesting starch possessed by the 

 embryo plant has been brilliantly demonstrated by van Tieghem,' 

 who found that the embryo removed from the seed of the Marvel 

 of Peru {Mirabilis jalapa) was distinctly nourished if placed in 

 an artificial seed made of starch paste. He found that the starch 

 paste was actually corroded by the young plant, proving that a 

 digestive ferment had been at work. 



This wonderful experiment is of special interest as proving 

 that the digestive ferment is a product of the young plant itself, 

 just as the digestive juice of an animal is a secretion from its 

 stomach. It is indeed a striking thought that whether we grind 

 up a grain of wheat to flour and eat it ourselves as bread, or 

 whether we let the seed germinate, in which case the young plant 

 eats it, the process is identically the same. 



The power of storing up food in a fixed condition and utilis- 

 ing it when required is a most important function both in 

 animal and plant physiology. And just as this utilisation 

 is seen in the seed to be brought about by a ferment — 

 by a digestive process — so probably wherever the transfer- 

 ence or utilisation of food stores occurs it is effected by 

 ferments. If this be so it would seem that the processes of 



' A Lecture delivered at the London Institution on March 11 by Francis 

 Darwin, M.B. 



* Deutsck. chem. Geselhch., 1874 ; Botanische Zeiiuitg, 1875, p. 565. 

 3 An. Sc. Nat., 1873, xvii. p. 205. 



