88 BOTANY. 



like this one, have the male and female reproductive organs on 

 distinct plants, are said to be " dioecious. 77 



A microscopical examination of the stem and leaves shows their struct- 

 ure to be very simple. The former is cylindrical, and composed of nearly 

 uniform elongated cells, with straight cross-walls. The leaves consist of a 

 single layer of small, roundish cells, which, like those of the stem, contain 

 numerous rounded chloroplasts, to which is due their dark green color. 



The tissues are developed from a single apical cell, but it is difficult to 

 obtain good sections through it. 



The antheridia are borne singly at the bases of the leaves on the special 

 branches already described (Fig. 53, A, an.). By carefully dissecting with 



an.- 



FIG. 53. A, end of a branch from a male plant of Madotheca. The small side 

 branchlets bear the antheridia, x 2. B, two young antheridia (an.), the 

 upper one seen in optical section, the lower one from without, x 150. C, a 

 ripe antheridium, optical section, x 50. D, sperm cells with young sperma- 

 tozoids. E, ripe spermatozoids, x 600. 



needles such a branch in a drop of water, some of the antheridia will 

 usually be detached uninjured, and may be readily studied, the full-grown 

 ones being just large enough to be seen with the naked eye. They are 

 globular bodies, attached by a stalk composed of two rows of cells. The 

 globular portion consists of a wall of chlorophyll-bearing cells, composed 

 of two layers below, but single above (Fig. 53, C). Within is a mass of 

 excessively small cells, each of which contains a spermatozoid. In the 

 young antheridium (.4, an.) the wall is single throughout, and the central 

 cells few in number. To study them in their natural position, thin longi- 

 tudinal sections of the antheridial branch should be made. 



When ripe, if brought into water, the antheridium bursts at the top into 



