634 The Outline of Science 



Significance of the Seed 



The seed is generally considered the reproductive body of 

 the flowering plant, but if we consider the process outlined above 

 we see that the true reproductive bodies are the egg-cell and the 

 sperm-cell. When the egg-cell is fertilised by the sperm-cell the 

 initiation of a new individual is complete. All subsequent events 

 are stages in the development of that individual; the seed is 

 merely a phase, at which development has been temporarily 

 arrested. 



This arrest, the formation of a seed, has two functions. It 

 provides for a dormant period and it provides for distribution. 

 Delicate leaves and shoots are not fitted to withstand extreme 

 conditions, whether the rigours of the northern winter or the 

 prolonged drought of more arid climates. The resistant leaves 

 of the evergreens persist through the cold months, but broad- 

 leaved trees shed their leaves and present bare branches to the 

 storms; herbaceous plants die down, persisting underground as 

 root-stock, rhizome, and bulb, buried deep from the cold. But 

 the seed is the most striking resting phase in the plant's life- 

 history. Dried up, its vital activities are reduced to a minimum ; 

 its close-textured coats protect it; it can resist temperatures far 

 below any occurring in the coldest winter; it can withstand con- 

 siderable heat; many seeds preserve their life for decades. The 

 seed can carry the plant over the most unfavourable conditions of 

 nature; for many plants it is the only resting and resistant stage. 



As important is the function of distributing the individuals 

 of the race. Fixed in the soil as soon as it germinates, the plant 

 can travel only at this specialised stage of its career. So the ripe 

 seed is cast loose from its parent. 



10 

 The Travels of Plants 



Plants travel in many ways. As the pod of the broom ripens, 

 the drying tissues contract at different rates, and internal strains 



