146 PREPARATION OF OBJECTS FOR THE MICROSCOPE. 



ions in the history of plant growth. As you know, there is in 

 plants almost as complete a circulation of fluids as in our own 

 bodies. The sap travels up from the roots through the capillary 

 tubes which are grouped in these fibro- vascular bundles, and 

 from them passes out through the veins of the leaves. At the 

 tip end of the veins it turns into another set of tubes under- 

 neath, and follows its course backward, gradually descending 

 towards the roots again, through cells between the bark and the 

 wood, where it leaves its deposit of formed material. The 

 capillary tubes of the vascular bundles were first and originally 

 formed as rows of large cells placed one on top of another. 

 Afterwards the partition walls which separated the cells were 

 absorbed and they became perfect tubes. Then on the inside of 

 these tubes were deposited closely coiled spiral threads, sometimes 

 rings, and sometimes again more open spirals, running in opposite 

 directions and crossing each other, forming what are called the 

 spotted ducts. But the spiral tubes, or tissues as they are called, 

 are certainly the most remarkable structures in the vegetable 

 economy. They are larger and more numerous in the castor oil 

 plant than in any other that I know of. But even in that plant, 

 it is as if wire, far finer than any silk or spider-web fiber, had 

 been closely wound around a form more slender than the finest 

 cambric needle, and then these coils had been laid away in groups 

 or bundles of twenty or more in the woody tissues next to the 

 pith cells. But now comes the puzzling question of how these 

 spiral tissues or threads were formed. By what laws of growth, 

 or by what natural process were these strange and complicate 

 structures built up? The botanist has not yet been able to 

 find it out. 



I may show you also this evening the remarkable glandular 

 organs, called the mushroom glands, of certain insectivorous 

 plants, which glands are said to secrete a gastric juice that 

 digests the bodies of insects, and which afterwards absorb the 

 products of that digestion. They are found on the upper sur- 

 face of the leaves, where they fulfill this extraordinary function. 

 But what is very strange, they also follow up the stem of the 

 flower, and are most beautiful and abundant on the outer leaves 



