THE LIFE CYCLE 



337 



Study 40. Observations on asexual reproductive methods. 



Materials for this study are almost limitless in number 

 and variety, and those mentioned below are suggested 

 merely as types. 



Study and compare together a few 

 special reproductive bodies, such as the 

 "gemmules" of the common greenhouse 

 liverwort, Marchantia, the frond bulbs of 

 , the bladder fern (Cystopteris bulbifera) , the 

 *^ "bulbils" of the tigec lily, the "sets" of the 

 onion, the tubers of the potato, etc., etc. 



Study the swarm spores of Drapernaldia 

 (fig. 187), or of Cladophora (in which they 

 are produced in great numbers in single 

 terminal cells), or of any of the water 

 molds. 



Study and compare together the stato- 

 blasts of such forms as Plumatella and 

 Pectinatella among bryozoans and of 

 Spongilla and Heteromyenia among fresh 

 water sponges; prepared slides will prob- 

 ably be needed for this. If some sponge 



Fig. 190. Polv- -^ . h- & 



embryonyin statoblasts can be gcrmmatcd under obser- 



Po lygnotus . . 



(after Marchai). vation, their multicellular nature will be 



a, the egg; b, 



the same after apparent. 



repeated divi- r 1 • 



sions of its nu • The rccord of this study may consist 



cleus; c, the 



same after the m nOtCS On and llStS of the objects ex- 

 development of . . 1 , , 



separate em- ammcd, together with sketches of some 



bryos from each 

 of the parts (de- of them 

 tails indicated 

 diagramm a t i - 

 cally in but two, 

 and these at dif- 

 ferent stages of 

 progress) . 



Polyembryony. — This is another kind of 

 asexual method of increase, that is even 

 more different in kind from the two 

 preceding than they are from each other. In certain 

 parasitic insects of the order Hymenoptera, the eggs 



