146 LABORATORY STUDIES OF THE FRUIT 



of which would have a chance of germinating upon the plot of ground 

 occupied by the parent, unless carried elsewhere. Take as an example 

 the Cranberry, studied in Exercise XXXV. Allow fifty berries to a 

 single bush, and multiply by the number of seeds actually observed 

 in one berry. The resulting product represents the possible number 

 of seedlings upon less than a square yard of ground. 



That even one seedling should occupy part of the soil held by the 

 parent plant would evidently be disadvantageous to both. Accord- 

 ingly, plants exhibit a great variety of devices by which the service 

 of various agencies is secured for the dispersal of the seeds. The 

 means of dissemination may be (1) some feature of the coat of the 

 seed itself, (2) some special character, construction, or outgrowth of 

 the pericarp. The first case has been seen in the Milkweed ; the 

 second remains to be studied in more detail. 



Bladder Nut. — Examine the bladdery fruit before dehiscence, not- 

 ing (1) the morphology of the pericarp, (2) the number of carpels, 

 and (3) the relative size of the pericarp and the seeds. Place the 

 fruit on the table. Blow it about. The object of the inflated peri- 

 carp becomes apparent. 



Draw^ the fruit, natural size. Indicate in dotted line the position 

 and size of the seed. 



Curled Dock. — With a lens examine the three-wdnged and coarsely 

 veined parts, each bearing at its base a granule resembling a seed. 

 They are persistent sepals, and are closely appressed. Hidden between 

 them is the three-angled achene (dry pericarp, containing a single 

 seed). The dispersal apparatus here comes from the calyx. Xote 

 how readily the fruit is driven by a mere breath. 



Draw the fruit, with one sepal removed to show achene, magnified 

 about eight diameters. 



Bur Marigold. — The barbed bristles, well seen with the lens, are 

 morphologically the border of the calyx, the low^er part of which is 

 adherent to the pericarp. What is the mode of dissemination ? 



Draw^ the fruit, magnified about four diameters. 



Witch-hazel. — Notice : — 



(1) The pericarp proper, with the old calyx surrounding the lower 

 half. (2) The partial splitting at the tips of unopened fruits. (3) The 

 number of cells (locul'i) in the opened capsules. (4) The mode of 

 dehiscence. The locuU are split open along the median line in each 

 case. This is lociilicidal dehiscence. (5) The backward curving of the 

 open jaw^s. (0) The very hard, smooth inner surface of the locuii, and 

 the similar surface of the seeds, which indeed makes it rather difficult 

 to hold them securely between finger and thumb. (7) Cut away the 

 calyx and the outer, softer layer of the pericarp. It will be seen that 

 the inner and immediate receptacle of the seeds is a bony and rather 

 thick-w^alled double case. There was originally one seed in each 



