Heterospory and seed habit

1. HETEROSPORY AND SEED HABIT
PRESENTED BY:-
PayalS.Chaudhari
M.sc Sem 1(botany)
Paper : CBO-402
Department of Life Sciences,
H.N.G.U PATAN

2. CONTENT
 INTRODUCTION
 HETEROSPORY
 SEED HABIT

3. INTRODUCTION
Heterospory is considered to be a
pre-requisite to seed formation,in
addition to heterospory the seed
plants show the following
characteristic's that have led to the
formation of the seed.

4. HETEROSPORY
 The sporangia show greater specialization that
those of ferns.
 They are differentiated into micro and
megasporangia.
 The microsporangia posses microsporangia
whereas megasporangia contain megaspores in
them. Each microsporangium contains a large
number of microspores whereas each
megasporangium possesses usually only four
megaspores.
 The condition of the production of two kinds of
dissimilar spores,differing in shape and size in the
same species is termed heterospory.

5.  When one kind of
spores are present,
viz., Equisetum and
ferns, the condition is
called homospory.
 According to modern
pteridologists the
heterospory is found in
seven genera-
Selaginella, Isoetes,
Marsilea ,Salvinia,
Azolla, Regnellidium
and Pilularia.

6.  Here one thing can be noticed that the
microspores develop male female
gametophytes which may also be called as
micro gametophytes and mega gametophytes.
 In the case of homospory the sex can be
differentiated only at the gametophyte stage,
but here the sex may be differentiated even at
the saprophytic stage by the presence of small
and large sized microspores which form
antherozoids and eggs respectively.
 The differentiation of microspores and
megaspores and their dependence upon the
sporophyte has some advantages.

7. Seed habit
 The condition of heterospory in selaginells
constitute one of the very important phases
in the evolution of the plants.
 In certain species of selaginella only one
megaspore develops within the mega
sporangium.
 The highest evolved species, that is, S. apoda
has advanced almost upto the rank of a seed
plant.

8.  Here, the megaspore remains within the
sporangium; it itself fertilizes and such way for
the first time the gametophyte of selaginella
show complete dependence of the gametophyte
upon sporophyte as in angiosperms.
 Biological importance of heterospory: The
phenomenon of heterospory is of great
Biological advantage due to the fact that a
large megaspore which contains female
gametophyte derives its food the sporophyte,
and is independent of the external conditions as
might interfere with the growth of a free living
gametophyte.

9.  In brief, the origin of seed habit is associated
with the following important prerequisites :
1. The production of two types of spores (i.e.,
heterospory).
2. The retention and germination of the
fertilization of the egg and embryo formation
which is still within germinating megaspore.
3. Development of only one megaspore per
megasorengium.

10. Reference
* Botany for degree students - pteridophyta
by:Vasishtha B.R
Sinha A.K.
Singh V.P
*www.google.com

11. THANK YOU