TRILLIUM 183 



tive probabilities of self-pollination and cross- 

 pollination. 



/. Non-sexual Reproduction: 



1. Non-sexual reproduction in Trillium is confined to 

 the growth of the persistent, underground rhizome. 

 This organ is thick and fleshy, serving for the storage 

 of food. 



2. Note the ridges and scars on its surface. 



3. What develops each year at the growing end? 



4. A plant that is continued indefinitely, from year to 

 year, by means of a persistent root or stem, or both, 

 is a perennial; one that persists for two years only, 

 setting seed and dying at the end of the second sea- 

 son is a biennial, plants that set seed and perish at 

 the end of one season are annuals. Name illus- 

 trations of each of these three classes of plants. 



K. Sexual Reproduction: 



1. Micros pores. 



(a) Mount in clearing fluid (or water) on a slide 

 some of the pollen from an anther. 



(b) Observe (first under low, then under high power) 

 the individual pollen-grains. Describe their 

 color and shape, and note the network of 

 ridges on the surface of each. 



(c) By carefully focusing on individual grains there 

 may readily be detected in some of them one 

 nucleus, in others, two. Those in the one- 

 nucleate stage are mature microspores. 



2. Male gametophyte. The division of the microspore- 

 nucleus is the first stage in the germination of the 

 spore. To what do microspores, when they ger- 

 minate, give rise? What, therefore, is the homol- 

 ogy of the bi-nucleate pollen-grain? 



(a) The larger nucleus is the tube-nucleus, and 



