12 THE CULTURE OF POT-PLANTS 



to the time that growth ordinarily begins to slacken, not 

 afterwards. Treat flowering plants in the same way, except 

 that feeding should not commence until the flower-buds 

 can be seen. 



Don't experiment on your plants with strong food if you 

 wish them to remain healthy. They may live in spite of 

 being dosed with such things as tea and castor oil (see 

 Preface). They could not live because of them. 



Finally, do not attach any importance to the claims made 

 in advertisements that certain patent fertilisers have marvellous 

 properties. If they contain nitrate, phosphate, and potash 

 in soluble form and in the right proportions, they may be 

 considered complete plant foods ; but their value lies solely 

 in these ingredients, and any other fertiliser containing the 

 same things in soluble form in the same proportions is quite 

 as good. This might seem to rule out certain bacterial 

 preparations which are on the market. They, however, 

 are not plant foods. All that is put forward on their behalf 

 is that under certain conditions they enable plants to obtain 

 nitrate from the air, and thus reduce the amount which need 

 be added to the soil. 



We have briefly considered the soil and its constituents 

 in connection with the growth of plants. The air plays 

 a scarcely less important part in their development, for from 

 it they obtain the carbon which enters largely into their 

 composition. They cannot obtain it in any other way. 

 There may be plenty of organic matter in the soil, but, as 

 it decomposes, the carbon in it escapes in the form of 

 carbonic acid gas ; while if we put soot or charcoal in the 

 ground, it cannot be absorbed by the roots, for both are 

 quite insoluble. 



The materials which the roots can absorb are, as 

 previously stated, soluble nitrate, phosphate, and potash. 

 These pass upwards into the leaves, which, by means of the 

 tiny openings on their surfaces (the stomata), are capable 

 of absorbing air and abstracting some of the carbonic acid 

 from it, and there, under the influence of the sunlight, they 

 are all acted on by the green colouring principle, the 



