PBOTOPLASM 23 



cation with the protoplasm in the neighbouring cells. It is supposed 

 that thin microscopic strands of protoplasm pass through the cell 

 walls from one protoplasmic mass to another, and also that the fluid 

 from a well-filled or turgid cell is diffused through the cell walls into a 

 comparatively empty one by a process which has been termed osmosis 

 or endosmosis, and that in this way the cell-sap is drafted to the outer- 

 most points of the shoots of plants no matter how tall. As the proto- 

 plasm in each cell is therefore dependent for its support on the food 

 dissolved in the cell-sap it naturally follows that no solid substance can 

 possibly enter as such into the system of a plant. The protoplasm is 

 formed, or forms itself, out of the food which has been absorbed in a 

 liquid state, and it then proceeds to build up the various tissues of the 

 plant which we know as shoots, stems, leaves, flowers &c. When the 

 liquid or watery sap in the cells becomes excessive it is exhaled or 

 breathed out into the atmosphere in the form of vapour by means of 

 the pores of the leaves referred to below under ' Transpiration ' at 

 p. 34, and fresh supplies as wanted are absorbed by the roots, but 

 only under favourable climatic conditions. To sum up, the whole 

 plant is dependent on the work of the protoplasm, and so long as this 

 continues to perform its functions, so long will the plant live and 

 produce in due course its flowers and fruits. Anything therefore that 

 tends to interfere with the work of the protoplasm, such as too much 

 heat or cold, too much drought or moisture, too much light or shade, 

 also stops the growth of the plant, and until proper conditions are 

 restored the plant is likely to die because the protoplasm cannot perform 

 its work in a satisfactory manner. 



The great aim of the gardener, therefore, is to choose the most 

 favourable conditions for his plants so that there will be no interference 

 or check to the mysterious work carried on within the cell walls by the 

 protoplasm. If a plant comes from a tropical climate, he endeavours to 

 imitate the natural warmth by growing it in a hothouse, as he very 

 soon discovers by the drooping and withering leaves and stems that a 

 cool temperature will be injurious. In the same way plants from 

 cold regions will be injured by excessive heat. As this work, however, 

 only deals with plants which will grow in the open air in our own 

 climate, the reader need not concern himself much about artificial heat, 

 although he will find many cases in which he is advised to use hotbeds 

 for raising seeds &c., and to place his plants in the warmest and sunniest, 

 in the coolest and shadiest, in the driest or dampest positions in his 

 garden ; but these instructions are all based upon this one principle 

 of placing a plant under the circumstances most favourable to the work 

 to be performed by the protoplasm in the cells. 



