10 STUDY OF COMMON PLANTS. 



far met with ? How are they recognized ? Mention cases 

 where you have found them associated with aleurone.^ 



Protection. 



I. Examine an orange with reference to the protection 

 of the embryos. Make a transverse section of the fruit, 

 ajid note carefully all the protective arrangements. 



II. Study an apple in the same way. 



III. Compare a number of commercial "nuts"; e.g. 

 almond, chestnut, peanut, hickory nut, Brazil nut. Which 

 are the most effectually protected ? How do they compare 

 with other fruits in this respect ? 



IV. Make a transverse section of a grain of Indian corn 

 and examine the pericarp microscopically. Notice the 

 multiplication of thick-walled cells and their arrangement. 

 Draw. 



V. After observing as many other seeds as are obtain- 

 able, summarize your observations of the ways in which 

 the embryo is protected against mechanical injuries, wet- 

 ting, destruction by animals, attacks of fungi, etc. Are 

 any that you have examined poorly protected ? ^ 



Dispersal. 



I. Examine the seeds of common milkweed, Asclepias 

 Cornuti, Decaisne. Compare those of the trumpet creeper, 

 Tecoma radicans, Juss, and those of the catalpa. 



II. Study as many as can be obtained of the following : 

 Seeds of willow or poplar ; fruits of elm, birch, maple, ash, 

 clematis, hop tree (^Ptelea), iron-wood ( Ostrya or Oarpi- 



1 Cf. Sachs, Physiology of Plants, pp. 323-340. 



2 Cf . De Candolle, Origin of Cultivated Plants, p. 395. 



