316 INTRODUCTION TO CYTOLOGY 



of Hieracium it has been found (Rosenberg 1906) that adventitious 

 diploid embryo-sacs are developed in the nucellus: these plants 

 are also apogamous. [In Marsilia Drummondii, which Shaw 

 (1897) and Nathansohn (1909) had shown to be apogamous, Stras- 

 burger (1907) found that, although normal reduction occurs in 

 some of the megasporocytes, giving spores with 16 chromosomes, 

 other megasporocytes undergo two divisions neither of which is 

 reductional: the first division is homceotypic in character and the 

 second is an additional vegetative mitosis without a homologue 



FIG. 126. 



A, gametophyte with antheridium (anth.) and rhizoids (r) arising aposporously from 

 tissue of sorus in Polystichum angulare var. pulcherrimum; sp, sporangia. X 70. (After 

 Bower.) B, gametophyte with archegonia arising from tip of pinnule in Polystichum. 

 X 10. (After Bower.) 



in the normal cases. The resulting spores are therefore diploid, 

 and ooapogamy follows.] 



Eu-apospory: no spore is formed of this there are two varieties: 

 (a) With meiosis: this occurs in some Thallophyta which form no 

 spores; the sporophyte of the Fucacese bears no spores, con- 

 sequently meiosis takes place in the developing sexual organs. 

 The Conjugate Green Algae also have no spores, meiosis 

 taking place in the germinating zygospore which develops 

 directly into the sexual plant. 



