15. REPRODUCTION. 49 



developed from the cortical tissue of the root or stem bearing 

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

 veloped exogenously ; those of Cuscuta, endogenously. They con- 

 tain vascular tissue. 



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. 

 JBryophyllum calycinum, many Ferns), the adventitious buds de- 

 velope 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 gemma?. In a few cases the 

 gemmae are unicellular, as those of some Algae, Fungi, and Hepaticae. 

 In other plants, multicellular gemmae are produced : as in other 

 Hepaticae where they are developed in special receptacles (cupules) 

 on the upper surface of the thallus (Lunularia, Marchantia), or on 

 the margin of the leaves. In some Mosses flattened gemmae are 

 produced in receptacles formed of leaves at the apex of the shoot, 

 as in Tetrapliis pellucida, and Aulacomnion androgynum : and 



