Chapter 19, Problem 39A

Summary Introduction

To analyze : 

The environmental conditions that lead to the formation of spores by acellular slime molds.

Introduction :

The somatic phase of acellular slime molds is a diploid multinucleate plasmodium. It is characterized by the presence of wall-less multinucleated protoplasm covered by slime. It is also known as the feeding stage. Plasmodium creeps over the surface of the substratum with the help of pseudopodia and absorbs the organic food from the decaying organic matter. The growth of plasmodium is supported by low light levels and high humidity.

Explanation of Solution

When plasmodium reaches a certain stage of maturity and the supply of resources present in the environment of slime mold is nearly exhausted, the content of the plasmodium concentrates at one or more places to form sporophore. The sporophore bears one or more fruiting bodies or sporangia. 

Apart from nutritional stress, high levels of light and low humidity cause plasmodium to divert all its energy into the growth of sporangia. Sporangia contain numerous diploid nuclei that undergo meiotic division to form uninucleate spores that are covered by a cell wall.

Conclusion

The plasmodium bears fruiting bodies when there is nutritional stress, high levels of light, and low humidity. These unfavorable environmental conditions lead to the formation of spores.