16 



POPULAR ILLUSTRATIONS OF 



green parts of a plant contain a pigment called chlorophylle ; this 

 pigment especially attracts carbonic acid from the air during light 

 decomposes it, stores up the carbon, and allows the oxygen to go 

 free. This process is termed the "fixation of carbon/' and is per- 

 formed by the green parts of the plant alone. 



We are now prepared to go on in our history and to study the 

 next and final stage : The plant flowers and forms seed. 



There is nothing in the wide and glorious field of nature more 

 beautiful than the details to which I now draw your attention. 



The process of flowering and forming seeds is essentially the same 

 in all flowering plants, although the details vary considerably. I 

 have said that a leaf is a lateral extension of the stem so a flower 

 is merely a modification of leaves without the power of extending 

 its central portion or axis. When a leaf bud opens, it grows by 



Fig. 7. Fig. 8. 



Figs. 7 and 8. Wheat-plant flowering (after Henslow). 



extending itself along a real or imaginary line termed its axis. A 

 flower bud, on the contrary, consists of certain organs growing and 

 increasing round a central fixed point or axis and if it varies from 

 this rule the flower is monstrous. 



Everybody knows that an ear of wheat consists of a spikelet con- 

 taining many separate flowers, each of which leaves behind it a 

 grain of wheat. Viewed singly these flowers are well represented in 

 Fig. 7. Those parts of the flower which are usually coloured are in 

 the wheat-plant green. They are two, and are known in the ripe corn 

 as the chaff. Botanically they are called " palea" one inner (a) and 

 one outer (b). If we tear these palese away we shall expose the 

 other parts of the flower, as shown in Fig. 8 ; a b constitutes what 

 is termed the pistil, and is formed of (a) the ovary and (s s) the two 

 styles, which at the end have a surface which secretes a sticky fluid, 

 and is termed the stigma (b b). It will be observed that the styles 



