15.] CHAPTER II. SPECIAL MORPHOLOGY OF THE MEMBERS. 67 



them. Those of Rhinanthus, Thesium and Orobanche, are de- 

 veloped exogenonsly; those of Cuscuta, endogenously. They 

 contain vascular tissue. 



B. REPRODUCTIVE ORGANS. 



15. Reproduction. Reproduction consists essentially in 

 the development of one or more new organisms from the whole or 

 from a part of the protoplasm of a parent organism. 



This may be effected either by the separation of a member or 

 a portion of the body, which, by developing the missing members, 

 constitutes a new individual ; or by the production of special re- 

 productive cells termed spores. Two modes of reproduction are 

 therefore distinguishable : vegetative multiplication, and spore- 

 reproduction. 



1. Vegetative Multiplication is essentially connected with the 

 process of growth. 



The simplest modes of this occur in unicellular plants. In 

 Pleurococcus, for instance, the cell divides into two, each of which 

 constitutes a new organism. In this case the parent ceases to 

 exist as an individual. In Yeast, the cell produces out-growths 

 each of which becomes an independent unicellular organism. In 

 this case the number of the progeny is not limited, and the parent 

 organism persists. This is termed multiplication by gemmation. 



In more complex plants vegetative reproduction is commonly 

 effected in this way, that the main axis of the shoot or of the 

 thallus, dies away: the branches thus become isolated and consti- 

 tute independent organisms. This occurs very commonly in the 

 protonema of Mosses, in the rhizomes of many Phanerogams, 

 etc. In those cases in which the leaves produce adventitious buds 

 (e.g. Bryophyllum calycinum, many Ferris), the adventitious buds 

 develope into independent plants after the leaf has fallen from the 

 plant bearing it. 



In many plants special organs for vegetative multiplication are 

 produced, which may be generally termed gemmce. In a few 

 cases the gemma3 are unicellular; as those of Vaucheria tuberosa 

 (ccenocyte), and of Monospora among the AlgaB, whic'i are the 

 terminal cells of branches; those of some Fungi (Mucorini, 

 Tremellineae, some Ascomycetes) where they are segments of 

 mycelial branches ; and those which are produced on the margins 

 of the leaves of Jungermannia ventricosa, Scapania nemorosa, and 

 other Hepaticse. 



