HOW PLANTS GROW. 



Fig. 1. 



now PLANTS GROW. 



BY TROFESSOR ASA GRAY, CAMBRIDGE, MASS. 



[We have already priven the hifjliest commendation in our power to Professor 

 Asa Gray's most himinoiis rudimentary work on botany, jnst issued l)y Ivison <fe 

 Phinney, New York, tlic title of which is First Lessons in lioUniy and J'er/etalife 

 Pln/siolorjij ; but beinir anxious to enlist in its favor the whole of our readers, and 

 through their influence to endeavor to have it introduced into schools and col- 

 leges, we applied to the author for permission to coi)y one of the chapters. For 

 that purpose we selected the Twenty-Second Lesson (" How Plants Grow"), and 

 present the necessary cuts to illustrate this interesting topic, the theory of which 

 is so lately adopted by the scientific world as to be taught only in books of the 

 last quarter of a century.] 



" 380. A plant grows from the seed, and from a tiny embryo like that of the Maple 

 (Fig. 1), becomes perhaps a large tree, producing every year a crop of seeds, to 

 grow in their turn in the same way. But how does the plant 

 grow ? A little seedling, weighing only two or three grains, 

 often doubles its weight every week of its early growth, and 

 in time may develop into a huge bulk, of many tons' weight 

 of vegetable matter. IIow is this done ? What is vege- 

 table matter ? Where did it all come from ? And by what 

 means is it increased and accumulated in y)lants ? Such 

 questions as these will now naturally arise in any inquiring 

 mind ; and we must try to answer them. 



" 38L Growth is the increase of a livinr^ thing in size and 

 suhstance. It appears so natural to us that plants and ani- 

 mals should grow, that people rarely think of it as requiring 

 any explanation. They say that a thing is so because it 

 ♦grew so. Still, we wish to know how the growth takes 

 place. 

 " 383. Now, in the foregoing Lessons, we explained the whole structure of the 

 plant, with all its organs, by beginning with the seedling plantlet, and following it 

 onward in its development through the whole course of vegetation. So, in attempt- 

 ing to learn how this growth took place, it will be best to adopt the same plan, 

 and to commence with the commencement — that is, with the first formation of a 

 plant, This may seem not so easy, because we have to begin with ]iarts too small 

 to be seen without a good microscope, and requiring much skill to dissect and ex- 

 hibit. But it is by no means difficult to describe them ; and with the aid of a 

 few figures, we may hope to make the whole matter clear. 



"383. The embryo in the ripe seed, is already a plant in miniature, as we have 

 learned in the Second, Third, and Twenty-First Lessons. It is already provided 

 with stem and leaves. To learn how the plant began, therefore, we must go back 

 to an earlier period still ; namely, to the formation and 



" 384. Growth of the Embryo itself. For this purpose, we examine the 

 ovule in the pistil of the flower. During, or soon after blossoming, a cavity ap- 

 pears in the kernel or nucleus of the ovule, lined with a delicate membrane, and 

 so forming a closed sac, named the embryo-sac. In this sac or cavity, at its upper 

 end (viz. at the end next the orifice of the ovule), appears a roundish little vesicle 

 bladder-like body, perhaps less than one thousandth of an inch in diameter 

 is the embryo, or rudimentary new plant, at its very beginning. Bu 



Germinating embryo of a 

 Maple. 



