HOW PLANTS LIVE AND WORK. 341 



great extent the action of the disease-producing germs^ and, as it has 

 been well said, " there is no reason, from the point of view of the 

 biologist, why these lowest plants should not be cultivated and 

 specialised as breeds and varieties for the service of mankind, as 

 the Peach and the Strawberry, the Wheat and the Cabbage, have 

 been." 



Lastly, one finds creeping about in tanyards, and on dead 

 leaves and rotting wood, naked pieces of protoplasm, often several 

 inches in size. Whether these organisms are plants or animals is 

 not definitely settled ; they are probably on the borderland of the 

 two kingdoms, and are chiefly interesting on account of the oppor- 

 tunity they afford of studying the activities of living protoplasm 

 on a large scale. 



V. — Evolution. 



In the preceding sections, sketchy as they necessarily have 

 been, enough has been said to indicate the vast diversity of struc- 

 ture among plants. The lowest plants consist of one cell only, 

 and they reproduce their kind by the simple method of splitting 

 up into two independent individuals, each of which resembles its 

 parent. Closely related to these are the forms which consist of 

 similar cells placed end to end. In such cases each cell has to do 

 all its own work, but as we examine more complex types we find 

 that different cells have different duties allotted them — a state of 

 things which is obviously of great advantage to the colony. This 

 division of labour becomes more and more marked as we ascend 

 the scale of plant life, until in the highly complex flowering plants 

 we find the principle carried out to a very perfect extent. Some 

 of the cells, those containing chlorophyll, prepare the food, and 

 thus act as the cooks of the community. To others is relegated 

 the duty of distributing the nutriment to the various centres of 

 activity. Other cells — which from their earliest days are most 

 carefully tended and nourished — are told off to provide new indi- 

 viduals, and thus to continue the race. Yet others act as nurses 

 for the young embryos, and feed them until they are sufficiently 

 developed to provide for themselves. 



It has been known for a long time that the gradually ascending 

 scale of complexity which is thus observable among living plants 

 is also to be found in fossil forms. The most recently formed 



International Journal of Microscopy and Natural Science. 

 Third Series. Vol. VII. y 



