STUDIES OF SEED-PLANTS 223 



many? Where are the seeds attached, and how many in each 

 cavity? Note the tough papery walls of these cavities; this is 

 the ovary-wall, commonly called the core of the apple. The fleshy 

 mass which forms the bulk of the edible part is really the thickened 

 receptacle of the flower. In the fleshy part, a short distance from 

 the seed-cavities, is a ring of dots, the cut-off ends of the fibro- 

 vascular bundles which carried the food into the developing apple. 

 How many dots are there and what relation is there between their 

 number and that of the seed-cavities and sepals ? In a longitudinal 

 section of apple cut from stem end to sepal end, the string-like nature 

 of these nbro-vascular bundles will be more evident ; they can be 

 pulled out much as you removed the strings from the pod of the bean 

 in an earlier lesson. Note that these bundles originate in the stem 

 of the apple and pass up to the sepals. 



Compare (optional) the fruits of pear, quince, and apple. 



Cucumber or Squash, Melon, Gourd. Examine a series of stages 

 showing development of cucumber flower into the fruit. These 

 may be collected in summer and preserved in formalin. Cut a cu- 

 cumber crosswise. How many seed-cavities do you find? Where 

 are the seeds attached? The rind and the fleshy mass outside of 

 the seed-chambers is derived from ovary-wall and receptacle. 

 Examine a cross section of an immature squash ; observe the seed- 

 cavities in the center, and the attachment of the seeds to placentas. 

 The region immediately outside the seed-cavities is the ovary-wall, 

 the remainder of the fleshy mass and the rind is derived from the 

 receptacle. In the watermelon the main bulk and the edible part 

 is the enlarged placenta. 



* 217. Dispersal of Fruits and Seeds. It is an interesting 

 fact that only by the scattering of fruits and seeds is it pos- 

 sible for most higher plants to become widely distributed. A 

 single plant of the Russian thistle may produce several hun- 

 dred thousand seeds. If all these seeds were to fall at the 

 base of the plant and there start to develop, it is very likely 

 that none of them would reach maturity, for they would 

 crowd and starve each other to death. Nature has pro- 

 vided against such a calamity and ensured the distribution 

 of the species, for the plant when mature assumes a ball-like 

 form, breaks off at the ground, and is rolled by the wind for 

 miles from the place where it grew, dropping its seeds as 



