At 05:49 AM 10/20/97 -0700, you wrote:
>At 9:22 PM -0400 10/17/97, Nancy Harrison wrote:
>>One of our instructors told me that "heterospory" now means
>>that the two types of spores are not necessarily different in
>>size, but always produce gametophytes of only one sex or the
>>other (dioecious, i.e.) so that mosses with dioecious gametophytes
>>are "heterosporous", etc. Is this the case? Our text (Campbell)
>>does not say this. But perhaps some major change has come
>>about. What then happens to plants with only one kind of
>>sporangium? What happens to "microspores and megaspores"?
>>Do we need more terminology tacked on now? Comments welcome! -NH
>>Nancy,
>>I never heard of this either and would be shocked if this
>were the current correct interpretation. I will be
>following replies with interest to see if there is anything
>authoritative.
>>ross
ross and Nancy,
Please don't take my answer as authoritative, but here goes: Richard
Bateman reviewed the history of definitions of the term heterospory in a
recent paper (1994, Biological Reviews 69:345-417). He defined heterospory
SENSU STRICTO as viable spore size bimodality. In doing this, he attempted
to remove the theoretical baggage of seed evolution from merely having
different sized spores. Additionally, he defined many other terms, some of
which I have not heard before. Thus, according to him, heterosporous plants
need not have sexes apportioned to different gametophytes. On the other
hand, some authors state that sexual separation is the only important point
(Bold et al. for example). Personally, I would go with Bateman's definition.
Doug
Douglas P. Jensen, Assistant Professor of Biology
PO Box 9615
Hollins College
Roanoke, Virginia 24020
(540)362-6549
djensen at hollins.edu
