6th. _Maiz tardio_, or, _de riego_; the most productive of all varieties, and that which is cultivated around the city of Mexico, and in many moist regions. It sometimes yields five hundred per cent. on the quantity planted. Maize succeeds best in Mexico in moist and warm climates; but it has the great advantage over the other cereal grains that it may be as successfully cultivated in this country in the _tierras calientes_, as in the _tierras frias_. Its highest limits here are from two to eight thousand feet above the level of the sea, and consequently the time required for ripening is different at different elevations. It varies from seven months to six weeks. The _diseases_ which sometimes affect or destroy this vegetable in Mexico, as well the animals that assail it, may be summed up as follows: 1. _La requitte_, a wasting blight which affects the maize where it is sown upon poor soil and is subjected to damp, cold weather soon after planting. 2. _El carbon_--a vegetable fungus growth, resembling carbon or coal, which appears in the ears and destroys them. This abortion in the fruit is believed to be produced by an insect. 3. _El hanjo_--a species of _uredo_, which forms itself in the ear and ruins it. The disease is generally known as _los Cuervos_. The animals and birds that attack corn are: 1. A sort of mole--_talpa_--which undermines the fields and destroy the young plants. 2. The _larvæ_ of _melolontha_, which not only seize the roots, but often destroy the stalks and ears. 3. Flocks of pilfering birds, with which the corn-fields are covered, if they are not carefully watched during the approach of harvest. Neither day nor night are the ears safe from the attacks of these pilferers; and, in order to protect the crop, watchmen are placed on high stages, overlooking the acres, whence the traveller constantly hears their shouts, during the day, or the crack of the warning whips, during the night. * * * * * Maize may be planted in Mexico at different periods of the year, especially in those districts in which, for nine months, there is always sufficient moisture. In the _tierra caliente_, the _rancheros_, cultivate, in this grain, the best spots lying near their dwellings. In the cooler districts they have two kinds of culture--one by irrigation, and another upon a dry soil. The latter mode is subdivided, by the Mexicans, into three kinds--the _humido_, _aventureso_, and _temporal_. In the first mode of cultivation the _Maiz tardio_, is sown, and it is usually found to be the most productive. A seeding made in a soil capable of preserving the winter's moisture and the humidity of the first spring rains, is called _siembra de aventureso_. In the _temporal_, a quickly ripening species of corn is planted--such as the _maiz cuarentino_--which may be cultivated either before or during the rainy season, from May to November.