iSS 



PLANT BIOLOGY 



thought they were productions of the dead matter upon which they 

 grew, but now we know that a mold, as any other plant, cannot 

 originate spontaneously ; it must start from something which is 

 analogous to a seed. The "seed " in this case is a spore. A spore 

 in iv be produced by a vegetative process (growing out from the 

 ordinary plant tissues), or it may be the result of a fertilization 

 process. 



Favorable conditions for the growth of f/ngi. — Place a piece 



z of bread under a moist bell jar and another in an uncovered 



place near by. Sow mold on each. Note the result from day to 



day. Moisten a third piece of bread with weak copper sulfate 



(blue vitriol) or mercuric chlorid solution, 



sow mold, cover with bell jar, note results, 



and explain. Expose pieces of different kinds 



of food in a damp atmosphere and observe 



the variety of organisms appearing. Fungi 



are saprophytes or parasites, and must be 



^-^s&fM&^fi^ provided with organic matter on which to 



grow. They are usually most abundant in 



moist places and wet seasons. 



Fig. 271. — Mucor Mold. — One of these molds {Mucor mu- 



mucedo, showing habit, cedo), which is very common on all decay- 

 ing fruits and vegetables, is shown in Fig. 

 271, somewhat magnified. When fruiting, this mold appears as a 

 dense mass of long white hairs, often over an inch high, standing 

 erect from the fruit or vegetable on which it is growing. 



The life of this mucor begins with a minute rounded spore 

 (a, Fig. 272), which lodges on the decaying material. When the 

 spore germinates, it sends out a delicate thread that grows rapidly 

 in length and forms very many branches that 

 soon permeate every part of the substance on 

 which the plant grows (6, Fig. 272). One of 

 these threads is termed a hypha. All the 

 threads together form the mycelium of the 

 fungus. The mycelium disorganizes the ma- 

 terial in which it grows, and thus the mucor 

 plant (Fig. 271) is nourished. It corresponds 

 physiologically to the roots and stems of other 

 plants. 



When the mycelium is about two days old, it begins to form the 

 long fruiting stalks which we first noticed. To study them, use a 

 compound microscope magnifying about two hundred diameters. 

 One of the stalks, magnified, is shown in a, Fig. 274. It consists 

 of a rounded head, the sporangium, sp, supported on a long, 



Fig. 272. — Spokes 

 OFMucor, some 

 germinating. 



