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1

Yes, it has very much to do with the poliploidy events. Specifically if you look at the grasses, most grasses that are diploid (eg., AA, BB), cannot hybridize, but in some rare events when they form polyploid (AAAA, BBBB), they can readily hybridize to form fertile progenies (AABB).


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http://en.wikipedia.org/wiki/Carbon_dioxide#Toxicity "In concentrations up to 1% (10,000 ppm), it will make some people feel drowsy.[83] Concentrations of 7% to 10% may cause suffocation, even in the presence of sufficient oxygen, manifesting as dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour. ... ...


2

The shedding of leaves has more to do with the condition of the leaf itself. When leaves become inefficient and unable to produce food and growth regulators, a process of abscission starts. Abscission a step in the planned senescence process within tree leaves. Senescence is a series of events that allow trees to conserve resources, prepare for a dormant ...


1

I am not sure what your question is but here is an example that may interest you. The three sunflower species Helianthus anomalus, H. deserticola, and H. paradoxus are all of hybrid origin of the same two "parent species" (H. annuus and H. petiolaris). Major ecological transitions in wild sunflowers facilitated by hybridization is a paper that will ...


2

One example of what you may consider to be a macroevolutionary change is a whole-genome-duplication, or polyploidy event. These are not uncommon in plants, and can promote speciation due to a reproductive barrier arising between the polyploid progeny and the diploid parents. You can find many papers about this topic, here is one from 2009: ...


5

The process of a deciduous plant losing its leaves seasonally is known as abscission. It occurs when a layer of cells known as the abscission zone elongate and weaken, causing the leaf to fall off. It is mediated mainly by the hormones auxin and ethylene. The functional purpose of abscission is to remove leaves when they are no longer producing a net gain ...


1

Each part of the Earth is divided into temperate zones depending on their latitude. Texas happens to be considered a Temperate Grassland. Temperate Grasslands are usually dominated by herbaceous vegetation. Because of where Texas is located on the Earth it has high summer temperatures which encourages fires. These fires help exclude woody vegetation such as ...


12

A quick google image search reveals that, indeed, Texas has quite lush forests. Remember that the state is extremely large (as compared to the Northeastern states, for example), and encompasses a huge variety of terrain, climates, rainfall amounts, etc. While the stereotypical view of Texas is rugged, dusty terrain: From: ...


2

For whether or not your assumption is correct, I have found the following (here), which states that sweetness indeed differs, as well as pH level: The bottom sections of ‘McIntosh’ apples were sweeter; whereas the bottom sections of ‘Jonagold’ were less crisp and more fruity. The bottom sections of both the ‘McIntosh’ and ‘Jonagold’ apples had ...


0

I looked in Taiz and Zeiger. Plant Physiology 5th ed and this is what I found: Plant growth is concentrated in localized regions of cell division called meristems. Nearly all nuclear divisions (mitosis) and cell divisions (cytokinesis) occur in these meristematic regions. In a young plant, the most active meristems are called apical meristems; they ...


0

A bud is capable of developing into a new individual while meristem can develop into any part of the individual. Buds can produce shoots, flowers, etc. while meristems have more variability - capable of developing into the tissues within the stem, a new individual, etc.


0

This book could be a good start: Botany by Mauseth. However if you don't have any knowledge about biology I suggest you to get starting with the basics of cellular biology. A good book could be "The cell" by Cooper, you can find it in electronic version. There are many books about cellular biology but I recommended this because it is complete and detailed ...


5

I think that the most important point has been given by CactusWoman, when (s)he says "Just because you cannot forsee a use for more "bulgy" spikes doesn't mean there isn't a use for them." In addition to that, I would like to say that several plants evolved traits that were beneficial at a time where other herbivores existed and that are now useless. Those ...


12

I think this is the Chinese Redbud (Cercis chinensis), see this image (from here):


4

Just because you cannot forsee a use for more "bulgy" spikes doesn't mean there isn't a use for them. Furthermore, natural selection isn't about producing perfect organisms, it's about selecting for traits that are "good enough". There is also more to evolution than natural selection. The phenomenon of genetic drift can cause a neutral or slightly ...



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