100 BIOLOGY 



each other is not by the structure and shape of the mycelium, 

 but rather by their method of producing spores. Penidllium 

 is one of the more common, but there are many other species 

 in which the spores are produced by different methods. Three 

 of these methods of spore formation are shown in Figure 42 

 C, E, and F. In some cases the spores are formed in a sac 

 called a sporangium, as at E. In others they are borne upon 

 a globular head, not inclosed in a sac; see F. Other species 

 show various methods; but in all cases the method of spore 

 formation is quite distinctive, and a careful microscopic study 

 of the different forms makes it possible to separate them into 

 species according to their methods of producing spores. 



Molds play a very important part in the life processes in 

 nature. The term mold is not a proper scientific designation 

 for these plants, but a popular name, covering a variety of 

 plants of similar form and structure, but with many different 

 botanical relations. That they belong to different groups is 

 proved by the fact already mentioned that they have different 

 methods of reproduction, some of them forming ascospores, 

 while others form spores by a process of conjugation, which, 

 as we shall learn later, is a type of sexual reproduction. 



LABORATORY WORK 



The laboratory work that can be done by an elementary class upon 

 karyokinesis is very limited. Mounted preparations should be furnished 

 by the instructor. For this purpose the young growing root tips of Podo- 

 phyllum are excellent. If these are collected in the spring and carefully 

 preserved, sectioned, and stained in iron haematoxylin, they will show all 

 stages of cell division. Longitudinal sections are. best, and they should be 

 studied with a 1/12 immersion objective to make out the details. By 

 patient study of a few sections thus prepared the various steps in karyoki- 

 nesis may be made out. 



If the instructor can furnish other examples of dividing cells the student 

 should make comparisons. Many tissues of animals and plants may be 

 utilized. 



