818 THE POPULAR SCIENCE MONTHLY. 



are simply causing the oxygen to recombine with these energetic vege- 

 table substances, and the result is, that we get once more the carbonic 

 acid and water with which we started. But we all know that such 

 burning yields not only heat, but also visible motion. This motion 

 is clearly seen even in the draught of an ordinary chimney, and may 

 be much more distinctly recognized in such a machine as the steam- 

 engine. 



At first sight, all this seems to have very little connection with 

 byacinth-bulbs. Yet, if we look a little deeper into the question, we 

 shall see that a bulb and an engine have really a great many points 

 in common. Let us glance first at a somewhat simpler case, that of a 

 seed, such as a pea or a grain of wheat. Here we have a little sack of 

 starches and albumen laid up as nutriment for a sprouting plantlet. 

 These rich food-stuffs were elaborated in the leaves of the parent pea, 

 or in the tall haulms of the growing corn. They were carried by the 

 sap into the ripening fruit, and there, through one of those bits of vital 

 mechanism which we do not yet completely understand, they were se- 

 lected and laid by in the young seed. When the pea or the grain of 

 wheat begins to germinate, under the influence of warmth and moist- 

 ure, a very slow combustion really takes place. Oxygen from the air 

 combines gradually with the food-stuffs or fuels call them which you 

 will contained in the seed. Thus heat is evolved, which in some 

 cases can be easily measured with a thermometer, and felt by the naked 

 hand as, for example, in the malting of barley. At the same time 

 motion is produced ; and this motion, taking place in certain regular 

 directions, results in what we call the growth of a young plant. In 

 different seeds this growth takes different forms, but in all alike the 

 central mechanical principle is the same : certain cells are raised visibly 

 above the surface of the earth, and the motive power which so raised 

 them is the energy set free by the combination of oxygen with their 

 starches and albumens. Of course, here, too, carbonic acid and water 

 are the final products of the slow combustion. The whole process is 

 closely akin to the hatching of an egg into a living chicken. But, as 

 soon as the young plant has used up all the material laid by for it by 

 its mother, it is compelled to feed itself just as much as the chicken 

 when it emerges from the shell. The plant does this by unfolding its 

 leaves to the sunlight, and so begins to assimilate fresh compounds of 

 hydrogen and carbon on its own account. 



Now, it makes a great deal of difference to a sprouting seed'whether 

 it is well or ill provided with such stored-up food-stuffs. Some very 

 small seeds have hardly any provisions to go on upon ; and the seed- 

 lings of these, of course, must wither up and die if they do not catch 

 the sunlight as soon as they have first unfolded their tiny leaflets ; 

 but other wiser plants have learned by experience to lay by plenty of 

 starches, oils, or other useful materials in their seeds ; and, wherever 

 such a tendency has once faintly appeared, it has given such an advan- 



