MICROSCOPE IN THE GARDEN. 19 



become marked, by their peculiar method of growth 

 (Fig. 40, PL 2). ' 



The vascular tissue of plants is either plain or 

 marked in its interior. If we examine the ribs of 

 leaves, the green stems of plants, or a longitudinal 

 section of wood, elongated fibres, lying side by side, 

 are observed (Fig. 48, PL 2). This is what is called 

 " ligneous" or "woody" tissue, and the greater part 

 of the wood and solid parts of plants are composed 

 of this tissue (Fig. 239, PL 8). The fibres lie in 

 bundles, and are divided from each other by cellular 

 tissue. This latter, in the woody stems of trees, 

 constitutes the " medullary rays," which are seen in 

 transverse sections of stems, extending from the 

 pith to the bark. The difference observable in the 

 distribution of the woody fibres and the medullary 

 rays renders the examination of transverse sections 

 of the stems of plants a subject of much interest 

 (Figs. 51, 52, 53, PL 3). In the transverse sections 

 of stems of most plants, large open tubes are ob- 

 served (Fig. 51, PL 3). These are called "ducts." 

 Such ducts may be well observed in the transverse 

 section of the common radish (Fig. 46, PL 2) and 

 other roots. These ducts are often marked by pores, 

 or dots, and are hence called " dotted ducts." 

 These dots are the result of deposits in the interior 

 of the tube of which the duct is formed, and a 

 great variety of such markings are found in the 

 interior of vascular tissue. One of the most common 

 forms of marked vascular tissue is that which is 

 called glandular woody tissue (Fig. 49, PL 3). This 

 kind of tissue is found in all plants belonging to 

 the cone-bearing, or fir tribe of plants. In order to 

 discover it, recourse need not be had to the garden 

 for growing plants, as every piece of furniture 

 made of deal wood will afford a ready means of 

 obtaining a specimen. All that is necessary to 

 c 2 



